publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2015-10-01 | 'Metal'-like transport in high-resistance, high aspect ratio two-dimensional electron gases | We investigate the striking absence of strong localisation observed in
mesoscopic two-dimensional electron gases (2DEGs) (Baenninger et al 2008 Phys.
Rev. Lett. 100 1016805, Backes et al 2015 Phys. Rev. B 92 235427) even when
their resistivity $\rho >> h/e^2$. In particular, we try to understand whether
this phenomenon originates in quantum many-body effects, or simply percolative
transport through a network of electron puddles. To test the latter scenario,
we measure the low temperature (low-$T$) transport properties of long and
narrow 2DEG devices in which percolation effects should be heavily suppressed
in favour of Coulomb blockade. Strikingly we find no indication of Coulomb
blockade and that the high-$\rho$, low-$T$ transport is exactly similar to that
previously reported in mesoscopic 2DEGs with different geometries. Remarkably,
we are able to induce a `metal'-insulator transition (MIT) by applying a
perpendicular magnetic field $B$. We present a picture within which these
observations fit into the more conventional framework of the 2D MIT. | 1510.00236v2 |
2016-07-28 | A Second-order Divergence-constrained Multidimensional Numerical Scheme for Relativistic Two-Fluid Electrodynamics | A new multidimensional simulation code for relativistic two-fluid
electrodynamics (RTFED) is described. The basic equations consist of the full
set of Maxwell's equations coupled with relativistic hydrodynamic equations for
separate two charged fluids, representing the dynamics of either an
electron-positron or an electron-proton plasma. It can be recognized as an
extension of conventional relativistic magnetohydrodynamics (RMHD). Finite
resistivity may be introduced as a friction between the two species, which
reduces to resistive RMHD in the long wavelength limit without suffering from a
singularity at infinite conductivity. A numerical scheme based on HLL
(Harten-Lax-Van Leer) Riemann solver is proposed that exactly preserves the two
divergence constraints for Maxwell's equations simultaneously. Several
benchmark problems demonstrate that it is capable of describing RMHD
shocks/discontinuities at long wavelength limit, as well as dispersive
characteristics due to the two-fluid effect appearing at small scales. This
shows that the RTFED model is a promising tool for high energy astrophysics
application. | 1607.08487v1 |
2016-12-14 | Successive spatial symmetry breaking under high pressure in the spin-orbit-coupled metal Cd2Re2O7 | The 5d-transition metal pyrochlore oxide Cd2Re2O7, which was recently
suggested to be a prototype of the spin-orbit-coupled metal [Phys. Rev. Lett.
115, 026401 (2015)], exhibits an inversion-symmetry breaking (ISB) transition
at 200 K and a subsequent superconductivity below 1 K at ambient pressure. We
study the crystal structure at high pressures up to 5 GPa by means of
synchrotron X-ray powder diffraction. A rich structural phase diagram is
obtained, which contains at least seven phases and is almost consistent with
the electronic phase diagram determined by previous resistivity measurements.
Interestingly, the ISB transition vanishes at ~4 GPa, where the enhancement of
the upper critical field was observed in resistivity. Moreover, it is shown
that the point groups at 8 K, probably kept in the superconducting phases,
sequentially transform into piezoelectric, ferroelectric, and centrosymmetric
structures on the application of pressure. | 1612.04577v2 |
2016-12-25 | Effects of Interstitial Oxygen and Carbon on Niobium Superconducting Cavities | We present results on the effects of interstitial oxygen and carbon on a
bulk-niobium superconducting radio-frequency cavity. Previous experiments have
shown that high-temperature (~800 $^\circ\text{C}$) nitrogen-doping plays the
dominant role in the reduction of the electron mean free path in the RF
penetration layer of niobium that leads to a decrease in microwave surface
resistance and a suppression the temperature-dependent component of the surface
resistance with increasing accelerating gradient. In this work, we show that
oxygen and carbon-doping has very similar effects on cavity performance,
demonstrating that these effects are not unique to nitrogen. The preparation
method used in the introduction of interstitial oxygen and carbon has the
advantage that it is done at lower temperatures than that of high-temperature
nitrogen-doping and does not require post-treatment electro-polishing. | 1612.08291v2 |
2017-06-06 | Topological Phase Transition Under Pressure in the Topological Nodal Line Superconductor PbTaSe$_2$ | A first-order-like resistivity hysteresis is induced by a subtle structural
transition under hydrostatic pressure in the topological nodal-line
superconductor PbTaSe$_2$. This structure transition is quickly suppressed to
zero at pressure $\sim$0.25 GPa. As a result, superconductivity shows a marked
suppression, accompanied with fundamental changes in the magnetoresistance and
Hall resistivity, suggesting a Lifshitz transition around $\sim$0.25 GPa. The
first principles calculations show that the spin-orbit interactions partially
gap out the Dirac nodal line around $K$ point in the Brillouin zone upon
applying a small pressure, whilst the Dirac states around $H$ point are
completely destroyed. The calculations further reveal a second structural phase
transition under a pressure as high as $\sim$30 GPa, through which a transition
from a topologically nontrivial phase to a trivial phase is uncovered, with a
superconducting dome emerging under this high-pressure phase. | 1706.01744v1 |
2018-02-21 | Optical transparency and electrical conductivity of single-wall carbon nanotubes and of intermediate filaments of porcine Müller cells | In the present study, we continue investigation of the high-contrast vision
in the inverted retina of the vertebrates eyes. We report a method of
separation and purification of porcine (Sus scrofa domestica) intermediate
filaments (IFs), extracted from the retinal M\"uller cells (MCs). We also
report experimental and theoretical methods of measurements and calculations of
the reduced resistivity and light transmission by the IFs and single-wall
carbon nanotubes (SWCNTs). The measured reduced resistivity values were
(3.1+-0.3)*10^-4 and (2.8+-0.2)*10^-4 Ohm m^-1 cm^2, respectively, being quite
close to those of typical metals. We report a method for measuring the light
energy transmission by the intermediate filaments and single-wall carbon
nanotubes. We found that these structures efficiently transfer light energy
along its axis, with the light reemitted at the other end of the structure. We
also report spectral selectivity of the IFs. The reported results demonstrate
that the assumptions we made in deducing the theory of high-contrast vision in
an inverted retina were correct and fully supported by the presently reported
experimental results. | 1803.07124v1 |
2018-04-27 | Effect of uniaxial stress on the magnetic phases of CeAuSb$_2$ | We present results of measurements of resistivity of \CAS{} under the
combination of $c$-axis magnetic field and in-plane uniaxial stress. In
unstressed \CAS{} there are two magnetic phases. The low-field A phase is a
single-component spin-density wave (SDW), with $\mathbf{q} = (\eta, \pm \eta,
1/2)$, and the high-field B phase consists of microscopically coexisting
$(\eta, \eta, 1/2)$ and $(\eta, -\eta, 1/2)$ spin-density waves. Pressure along
a $\langle 100 \rangle$ lattice direction is a transverse field to both of
these phases, and so initially has little effect, however eventually induces
new low- and high-field phases in which the principal axes of the SDW
components appear to have rotated to the $\langle 100 \rangle$ directions.
Under this strong $\langle 100 \rangle$ compression, the field evolution of the
resistivity is much smoother than at zero strain: In zero strain, there is a
strong first-order transition, while under strong $\langle 100 \rangle$ it
becomes much broader. We hypothesize that this is a consequence of the uniaxial
stress lifting the degeneracy between the (100) and (010) directions. | 1804.10539v2 |
2018-05-29 | Resisting collapse: How matter inside a black hole can withstand gravity | How can a Schwarzschild-sized matter system avoid a fate of gravitational
collapse? To address this question, we critically reexamine the arguments that
led to the "Buchdahl bound", which implies that the minimal size of a stable,
compact object must be larger than nine eighths of its own Schwarzschild
radius. Following Mazur and Mottola, and in line with other counterexamples to
the singularity theorems, we identify large negative radial pressure extending
to the gravitational radius as the essential ingredient for evading the
Buchdahl bound. Our results are novel although consistent with many other
investigations of models of non-singular black holes. It is shown in particular
that a large negative pressure in the framework of classical GR translates into
a large positive pressure once quantum physics is incorporated. In this way, a
Schwarzschild-sized bound state of closed, interacting fundamental strings in
its high-temperature Hagedorn phase can appear to have negative pressure and
thus the ability to resist gravitational collapse. | 1805.11667v2 |
2018-06-08 | Fluidity Onset in Graphene | Viscous electron fluids have emerged recently as a new paradigm of
strongly-correlated electron transport in solids. Here we report on a direct
observation of the transition to this long-sought-for state of matter in a
high-mobility electron system in graphene. Unexpectedly, the electron flow is
found to be interaction-dominated but non-hydrodynamic (quasiballistic) in a
wide temperature range, showing signatures of viscous flows only at relatively
high temperatures. The transition between the two regimes is characterized by a
sharp maximum of negative resistance, probed in proximity to the current
injector. The resistance decreases as the system goes deeper into the
hydrodynamic regime. In a perfect darkness-before-daybreak manner, the
interaction-dominated negative response is strongest at the transition to the
quasiballistic regime. Our work provides the first demonstration of how the
viscous fluid behavior emerges in an interacting electron system. | 1806.03231v2 |
2018-06-25 | Noise Measurements of High-Speed, Light-Emitting GaN Resonant-Tunneling Diodes | We report here the first RF noise measurements on two designs of n-doped
GaN/AlN double-barrier resonant tunneling diodes (RTDs), each having a
room-temperature negative differential resistance (NDR) and also strong near-UV
light emission. The measurements are made with a standard, un-isolated RF
receiver and calibration is made using a substitution-resistor/hot-cold
radiometric technique which works in the positive differential resistance (PDR)
region but not the NDR region. A high-quality InGaAs/AlAs double-barrier RTD is
used as a control sample and displays shot noise suppression down to
$\Gamma\approx$0.5 in the PDR region, as expected. The GaN/AlN RTDs display
both shot-noise enhancement and suppression in the PDR regions, but no obvious
sign of sudden shot-noise enhancement in the threshold bias region of light
emission. This supports the hypothesis that the holes required for light
emission are created by electronic (Zener) interband tunneling, not impact
ionization. Further the minimum shot-noise factor of $\Gamma\sim$ 0.34 suggests
that the GaN/AlN RTDs are acting like triple-barrier devices. | 1806.09270v1 |
2019-09-04 | High-field moment polarization in the itinerant ferromagnet URhSi | We report a high-magnetic-field study of the itinerant ferromagnet URhSi.
Magnetization and electrical resistivity were measured under magnetic fields
$\mu_0H$ up to 58~T applied along the directions $\mathbf{a}$, $\mathbf{b}$,
and $\mathbf{c}$ of the orthorhombic structure and temperatures $T$ ranging
from 1.5 to 50 K. For $\mathbf{H}\parallel\mathbf{b}$, pseudo-metamagnetism at
$\mu_0H_m\simeq30-40$~T is associated with a broad step in the magnetization
and a maximum in the resistivity. The properties of URhSi are discussed and
compared with those of the isostructural superconducting ferromagnets URhGe and
UCoGe and of the superconducting paramagnet UTe$_2$. | 1909.01810v2 |
2019-09-30 | Hall coefficient diagnostics of surface state in pressurized SmB6 | In this study, we report the first results of the high-pressure Hall
coefficient (RH) measurements in the putative topological Kondo insulator SmB6
up to 37 GPa. Below 10 GPa, our data reveal that RH(T) exhibits a prominent
peak upon cooling below 20 K. Remarkably, the temperature at which surface
conduction dominates coincides with the temperature of the peak in RH(T). The
temperature dependent resistance and Hall coefficient can be well fitted by a
two-channel model with contributions from the metallic surface and the
thermally activated bulk states. When the bulk of SmB6 becomes metallic and
magnetic at ~ 10 GPa, both the RH(T) peak and the resistance plateau disappear
simultaneously. Our results indicate that the RH(T) peak is a fingerprint to
diagnose the presence of a metallic surface state in SmB6. The high-pressure
magnetic state of SmB6 is robust to 180 GPa, and no evidence of
superconductivity is observed in the metallic phase. | 1909.13462v1 |
2014-10-06 | Memristive Threshold Logic Circuit Design of Fast Moving Object Detection | Real-time detection of moving objects involves memorisation of features in
the template image and their comparison with those in the test image. At high
sampling rates, such techniques face the problems of high algorithmic
complexity and component delays. We present a new resistive switching based
threshold logic cell which encodes the pixels of a template image. The cell
comprises a voltage divider circuit that programs the resistances of the
memristors arranged in a single node threshold logic network and the output is
encoded as a binary value using a CMOS inverter gate. When a test image is
applied to the template-programmed cell, a mismatch in the respective pixels is
seen as a change in the output voltage of the cell. The proposed cell when
compared with CMOS equivalent implementation shows improved performance in
area, leakage power, power dissipation and delay. | 1410.1267v1 |
2014-11-11 | Frequency-dependent phonon mean free path in carbon nanotubes from non-equilibrium molecular dynamics | Owing to their long phonon mean free paths (MFPs) and high thermal
conductivity, carbon nanotubes (CNTs) are ideal candidates for, e.g., removing
heat from electronic devices. It is unknown, however, how the intrinsic phonon
MFPs depend on vibrational frequency in non-equilibrium. We determine the
spectrally resolved phonon MFPs in isotopically pure CNTs from the spectral
phonon transmission function calculated using non-equilibrium molecular
dynamics, fully accounting for the resistive phonon-phonon scattering processes
through the anharmonic terms of the interatomic potential energy function. Our
results show that the effective room temperature MFPs of low-frequency phonons
($f<0.5$ THz) exceed $10$ $\mu$m, while the MFP of high-frequency phonons
($f\gtrsim 20$ THz) is in the range 10--100 nm. Because the determined MFPs
directly reflect the resistance to energy flow, they can be used to accurately
predict the thermal conductivity for arbitrary tube lengths by calculating a
single frequency integral. The presented results and methods are expected to
significantly improve the understanding of non-equilibrium thermal transport in
low-dimensional nanostructures. | 1411.2838v2 |
2014-11-12 | Acoustic (Ultrasonic) Non-Diffracting Beams: Some theory, and Proposals of Acoustic Antennas for several purposes | On the basis of suitable theoretical grounds, we study and propose Antennas
for the generation, in Acoustics, of Non-Diffracting Beams of ultrasound. We
start considering for instance a frequency of about 40 kHz, and foresee fair
results even for finite apertures endowed with reasonable diameters (e.g., of 1
m), having in mind various possible applications, including remote sensing.
Then, we discuss the production in lossy media of ultrasonic beams resisting
both diffraction and attenuation. Everything is afterward investigated for the
cases in which high-power acoustic transducers are needed (for instance, for
detection at a distance -or even explosion- of buried objects, like mines).
Keywords: Acoustic Non-Diffracting Beams; Truncated Beams of Ultrasound;
Remote sensing; Diffraction, Attenuation, Annular transducers, Bessel beam
superposition, High-power ultrasound emitters, Beams resisting diffraction and
attenuation, Acoustic Frozen Waves, Detection of buried objects, Explosion of
Mines at a distance | 1411.3340v1 |
2016-06-07 | Oscillatory Localization of Quantum Walks Analyzed by Classical Electric Circuits | We examine an unexplored quantum phenomenon we call oscillatory localization,
where a discrete-time quantum walk with Grover's diffusion coin jumps back and
forth between two vertices. We then connect it to the power dissipation of a
related electric network. Namely, we show that there are only two kinds of
oscillating states, called uniform states and flip states, and that the
projection of an arbitrary state onto a flip state is bounded by the power
dissipation of an electric circuit. By applying this framework to states along
a single edge of a graph, we show that low effective resistance implies
oscillatory localization of the quantum walk. This reveals that oscillatory
localization occurs on a large variety of regular graphs, including
edge-transitive, expander, and high degree graphs. As a corollary, high
edge-connectivity also implies localization of these states, since it is
closely related to electric resistance. | 1606.02136v3 |
2016-12-17 | Contact resistance between two REBCO tapes under load and load-cycles | No-insulation (NI) REBCO magnets have many advantages. They are
self-protecting, therefore do not need quench detection and protection which
can be very challenging in a high Tc superconducting magnet. Moreover, by
removing insulation and allowing thinner copper stabilizer, NI REBCO magnets
have significantly higher engineering current density and higher mechanical
strength. On the other hand, NI REBCO magnets have drawbacks of long magnet
charging time and high field-ramp-loss. In principle, these drawbacks can be
mitigated by managing the turn-to-turn contact resistivity (Rc). Evidently the
first step toward managing Rc is to establish a reliable method of accurate Rc
measurement. In this paper, we present experimental Rc measurements of REBCO
tapes as a function of mechanical load up to 144 MPa and load cycles up to 14
times. We found that Rc is in the range of 26-100 uOhm-cm2; it decreases with
increasing pressure, and gradually increases with number of load cycles. The
results are discussed in the framework of Holm's electric contact theory. | 1701.00447v2 |
2017-01-07 | A quantitative description of Nernst effect in high-temperature superconductors | A quantitative vortex-fluid model for flux-flow resistivity $\rho$ and Nernst
signal $e_N$ in high-temperature superconductors (HTSC) is proposed. Two kinds
of vortices, magnetic and thermal, are considered, and the damping viscosity
$\eta$ is modeled by extending the Bardeen-Stephen model to include the
contributions of flux pinning at low temperature and in weak magnetic fields,
and vortex-vortex collisions in strong magnetic fields. Remarkably accurate
descriptions for both Nernst signal of six samples and flux flow resistivity
are achieved over a wide range of temperature $T$ and magnetic field $B$. A
discrepancy of three orders of magnitude between data and Anderson's model of
Nernst signal is pointed out and revised using experimental values of $\eta$
from magnetoresistance. Furthermore, a two-step procedure is developed to
reliably extract, from the Nernst signal, a set of physical parameters
characterizing the vortex dynamics, which yields predictions of local
superfluid density $n_s$, the Kosterlitz coefficient $b$ of thermal vortices,
and upper critical field and temperature. Application of the model and
systematic measurement of relevant physical quantities from Nernst signal in
other HTSC samples are discussed. | 1701.01832v1 |
2018-11-08 | Temperature dependence of side-jump spin Hall conductivity | In the conventional paradigm of the spin Hall effect, the side-jump
conductivity due to electron-phonon scattering is regarded to be temperature
independent. To the contrary, we draw the distinction that, while this
side-jump conductivity is temperature independent in the classical
equipartition regime where the longitudinal resistivity is linear in
temperature, it is temperature dependent below the equipartition regime. The
mechanism resulting in this temperature dependence differs from the familiar
one of the longitudinal resistivity. In the concrete example of Pt, we show
that the change of the spin Hall conductivity with temperature can be as high
as 50%. Experimentally accessible high-purity Pt is proposed to be suitable for
observing this prominent variation below 80 K. | 1811.03229v6 |
2019-07-28 | Quantum critical fluctuations, Planckian dissipation, and compactification scale | The most striking result here is that the notion of Planckian dissipation is
also applicable to the $c$-axis resistivity of the high temperature cuprate
superconductors, and to my knowledge this aspect has not been previously
addressed. The derivation involves Kubo formula and does not require any
mechanism beyond a non-Fermi liquid assumption. The $c$-axis resistivity, in
its essential aspects, is discussed in the context of quantum critical point.
Finally, I consider a zero temperature problem with one of its spatial
dimensions compactified. The warning is that this compatification scale at the
quantum critical point behaves similarly to the finite temperature problem, but
obviously being at zero temperature there is no dissipation. | 1907.12163v2 |
2020-02-10 | Anomalous Nematic States in High Half-Filled Landau Levels | It is well established that the ground states of a two-dimensional electron
gas with half-filled high ($N \ge 2$) Landau levels are compressible
charge-ordered states, known as quantum Hall stripe (QHS) phases. The generic
features of QHSs are a maximum (minimum) in a longitudinal resistance $R_{xx}$
($R_{yy}$) and a non-quantized Hall resistance $R_H$. Here, we report on
emergent minima (maxima) in $R_{xx}$ ($R_{yy}$) and plateau-like features in
$R_H$ in half-filled $N \ge 3$ Landau levels. Remarkably, these unexpected
features develop at temperatures considerably lower than the onset temperature
of QHSs, suggesting a new ground state. | 2002.03964v2 |
2020-02-16 | Study of Position Sensitive Silicon Detector (PSD) for SiW-ECAL at ILC | We are developing position sensitive silicon detectors (PSDs) which have an
electrode at each of four corners so that incident position of a charged
particle can be obtained with signal from the electrodes. It is expected that
the position resolution of the electromagnetic calorimeter (ECAL) of the ILD
detector will be improved by introducing PSDs to detection layers. We have been
developing the PSDs for several years. In the previous production we found that
the charge separation is not optimally done due to the readout impedance. To
solve the issue, we produced new PSDs with higher surface resistance with an
additional resistive layer on the surface. We also implemented several
techniques to decrease position distortion and increase signal-to-noise ratio
which are essential for the optimal position resolution. The measurements on
the prototype sensors are ongoing, including radiation source measurement and
laser measurement using an ASIC for silicon pad detectors. | 2002.06534v2 |
2020-03-23 | Multi-Terminal DC Fault Identification for MMC-HVDC Systems based on Modal Analysis -- A Localized Protection Scheme | We propose a localized protection scheme based on modal analysis in
multi-terminal modular multilevel converter (MMC) based high voltage DC (HVDC)
systems. The paper addresses the issues of localized protection scheme based DC
fault identification, such as differentiating between external and internal
faults, classification of type of fault contingency i.e., pole to pole
(\textit{PTP}) or pole to ground (\textit{PTG}) for high impedance faults
(HIFs) in the system. The scheme works on equivalent network of multi-terminal
MMC-HVDC system for a DC fault, using phase-modal transformation to analyse
line-mode and zero-mode voltage across the current limiting reactor (CLR) for
different possible contingencies in the presence of fault resistance. The
protection scheme is validated to be reliable for HIFs and in the presence of
White Gaussian Noise (WGN) in measurement. The scheme operation is validated to
be intact for varying fault location, fault resistances and system transients. | 2003.10145v2 |
2022-01-31 | Accelerated 3D Electrical Resistivity Tomography with a Scalable Jacobian-free Approach | A Jacobian-free inversion method is presented to accelerate Electrical
Resistivity Tomography (ERT) for shallow aquifer characterization. The ERT
problem typically implements the adjoint state method to efficiently compute
Jacobian during the inversion. However, the adjoint state method needs
intrusive forward model code changes and may not be computationally scalable
with many observations especially when one performs 3D ERT surveys with dense
multi-electrode arrays. Here the Principal Component Geostatistical Approach
(PCGA), a fast and scalable Jacobian-free inverse modeling method, is applied
to solve a high dimensional data-intensive ERT problem. The PNNL's ERT
simulation software E4D was linked to the python interface pyPCGA without
intrusive code change and the example code is upload in a public repository.
The result in this study shows that high-resolution 3D subsurface
characterization is computationally feasible, which would have a great
potential for implementations in practice. | 2202.00059v1 |
2014-01-02 | Electrolyte gate dependent high-frequency measurement of graphene field-effect transistor for sensing applications | We performed radiofrequency (RF) reflectometry measurements at 2.4 GHz on
electrolyte-gated graphene field-effect transistors (GFETs) utilizing a tunable
stub-matching circuit for impedance matching. We demonstrate that the gate
voltage dependent RF resistivity of graphene can be deduced even in the
presence of the electrolyte which is in direct contact with the graphene layer.
The RF resistivity is found to be consistent with its DC counterpart in the
full gate voltage range. Furthermore, in order to access the potential of
high-frequency sensing for applications, we demonstrate time-dependent gating
in solution with nanosecond time resolution. | 1401.0381v1 |
2016-03-16 | The "ideal" tearing mode: theory and resistive MHD simulations | Classical MHD reconnection theories, both the stationary Sweet-Parker model
and the tearing instability, are known to provide rates which are too slow to
explain the observations. However, a recent analysis has shown that there
exists a critical threshold on current sheet's thickness, namely a/L~S^(-1/3),
beyond which the tearing modes evolve on fast macroscopic Alfvenic timescales,
provided the Lunquist number S is high enough, as invariably found in solar and
astrophysical plasmas. Therefore, the classical Sweet-Parker scenario, for
which the diffusive region scales as a/L~S^(-1/2) and thus can be up to ~100
times thinner than the critical value, is likely to be never realized in
nature, as the current sheet itself disrupts in the elongation process. We
present here two-dimensional, compressible, resistive MHD simulations, with S
ranging from 10^5 to 10^7, that fully confirm the linear analysis. Moreover, we
show that a secondary plasmoid instability always occurs when the same critical
scaling is reached on the local, smaller scale, leading to a cascading
explosive process, reminiscent of the flaring activity. | 1603.04995v1 |
2017-05-15 | Mathematical Analysis of the Probability of Spontaneous Mutations in HIV-1 Genome and Their Role in the Emergence of Resistance to Anti-Retroviral Therapy | $\textbf{Background:}$ High mutability of HIV is the driving force of
antiretroviral drug resistance, which represents a medical care challenge.
$\textbf{Method and Model Equation:}$ To detect the mutability of each gene
in the HIV-1 genome; a mathematical analysis of HIV-1 genome is performed,
depending on a linear relation wherein the probability of spontaneous mutations
emergence is directly proportional to the ratio of the gene length to the whole
genome length. \begin{equation*} {P_g}{S_i} =\frac{g}{G} \end{equation*}
$\textbf{Results:}$ $\textbf{tat}$, $\textbf{vpr}$ and $\textbf{vpu}$ are the
least mutant genes in HIV-1 genome. Protease $\textbf{PROT}$ gene is the least
mutant gene component of the polymerases $\textbf{pol}$.
$\textbf{Conclusion:}$ $\textbf{tat}$, $\textbf{vpr}$ and $\textbf{vpu}$ are
the best candidates for HIV-1 recombinant subunit vaccines or as a part of
$\textit{prime and boost}$ vaccine combinations. Also; the protease
inhibitor-based regime represents a high genetic barrier for HIV to overcome. | 1705.06132v1 |
2017-08-05 | Copper-oxide Nanowires based Humidity Sensor | This paper presents investigated results of copper-oxide nanowires used as a
humidity sensor. Copper-oxide nanowires films were grown over cross-comb type
gold electrodes on a SiO2 substrate using thermal annealing technique, and its
humidity sensitive characteristics were investigated through resistance across
the gold electrodes. These copper-oxide nanowires films revealed high
sensitivity and long-term stability with fast response time. It was found that
resistance across gold electrodes of the fabricated sensor decreases with
increase in humidity almost linearly on a logarithmic scale. It appears that
copper-oxide nanowires can be used as low-cost humidity sensor with high output
reliability and reproduction rate. The observations were carried out at room
temperature (RT) and relative humidity (RH) in the range of 6% to 97%. | 1708.01720v1 |
2018-08-03 | An All-Electric Single-Molecule Hybridisation Detector for short DNA Fragments | In combining DNA nanotechnology and high-bandwidth single-molecule detection
in nanopipettes, we demonstrate an all-electric, label-free hybridisation
sensor for short DNA sequences (< 100 nt). Such short fragments are known to
occur as circulating cell-free DNA in various bodily fluids, such as blood
plasma and saliva, and have been identified as disease markers for cancer and
infectious diseases. To this end, we use as a model system a 88-mer target from
the RV1910c gene in Mycobacterium tuberculosis that is associated with
antibiotic (isoniazid) resistance in TB. Upon binding to short probes attached
to long carrier DNA, we show that resistive pulse sensing in nanopipettes is
capable of identifying rather subtle structural differences, such as the
hybridisation state of the probes, in a statistically robust manner. With
significant potential towards multiplexing and high-throughput analysis, our
study points towards a new, single-molecule DNA assay technology that is fast,
easy to use and compatible with point of care environments. | 1808.01168v1 |
2018-08-23 | An explicit divergence-free DG method for incompressible magnetohydrodynamics | We extend the recently introduced explicit divergence-free DG scheme for
incompressible hydrodynamics [arXiv:1808.04669]. to the incompressible
magnetohydrodynamics (MHD). A globally divergence-free finite element space is
used for both the velocity and the magnetic field. Highlights of the scheme
includes global and local conservation properties, high-order accuracy,
energy-stability, pressure-robustness. When forward Euler time stepping is
used, we need two symmetric positive definite (SPD) hybrid-mixed Poisson
solvers (one for velocity and one for magnetic field) to advance the solution
to the next time level. Since we treat both viscosity in the momentum equation
and resistivity in the magnetic induction equation explicitly, the method shall
be best suited for inviscid or high-Reynolds number, low resistivity flows so
that the CFL constraint is not too restrictive. | 1808.08119v1 |
2019-08-13 | Study of Particle Multiplicity of Cosmic Ray Events using 2m$\times$2m Resistive Plate Chamber Stack at IICHEP-Madurai | An experimental setup consisting of 12 layers of glass Resistive Plate
Chambers (RPCs) of size 2\,m\,$\times$\,2\,m has been built at IICHEP-Madurai
(\ang{9;56;14.5}\,N \ang{78;00;47.9}\,E, on the surface) to study the long term
performance and stability of RPCs produced on large scale in Indian industry.
This setup has been collecting data triggered by the passage of charged
particles. The measurement of the multiplicity of charged particles due to
cosmic ray interactions are presented here. Finally, the results are compared
with different hadronic models of the CORSIKA simulation. | 1908.04589v5 |
2011-04-11 | Resistively detected nuclear magnetic resonance via a single InSb two-dimensional electron gas at high temperature | We report on the demonstration of the resistively detected nuclear magnetic
resonance (RDNMR) of a single InSb two-dimensional electron gas (2DEG) at
elevated temperatures up to 4 K. The RDNMR signal of 115In in the simplest
pseudospin quantum Hall ferromagnet triggered by a large direct current shows a
peak-dip line shape, where the nuclear relaxation time T1 at the peak and the
dip is different but almost temperature independent. The large Zeeman,
cyclotron, and exchange energy scales of the InSb 2DEG contribute to the
persistence of the RDNMR signal at high temperatures. | 1104.1826v1 |
2012-03-23 | Transport Measurements on Nano-engineered Two Dimensional Superconducting Wire Networks | Superconducting triangular Nb wire networks with high normal-state resistance
are fabricated by using a negative tone hydrogen silsesquioxane (HSQ) resist.
Robust magnetoresistance oscillations are observed up to high magnetic fields
and maintained at low temperatures, due to the eective reduction of wire
dimensions. Well-defined dips appear at integral and rational values (1/2, 1/3,
1/4) of the reduced flux f = Phi/Phi_0, which is the first observation in the
triangular wire networks. These results are well consistent with theoretical
calculations for the reduced critical temperature as a function of f. | 1203.5163v1 |
2015-04-03 | Energy-efficient hybrid spintronic-straintronic reconfigurable bit comparator | We propose a reconfigurable bit comparator implemented with a nanowire spin
valve whose two contacts are magnetostrictive with bistable magnetization.
Reference and input bits are "written" into the magnetization states of the two
contacts with electrically generated strain and the spin-valve's resistance is
lowered if they match. Multiple comparators can be interfaced in parallel with
a magneto-tunneling junction to determine if an N-bit input stream matches an
N-bit reference stream bit by bit. The system is robust against thermal noise
at room temperature and a 16-bit comparator can operate at roughly 416 MHz
while dissipating at most 420 aJ per cycle. | 1504.00952v2 |
2020-01-09 | Coupling loss at the end connections of REBCO stacks: 2D modelling and measurement | In high power density superconducting motors, superconducting tapes are
usually stacked and connected together at terminals to improve the current
capacity. When a parallel sinusoidal magnetic field is applied on this
partially coupled stack, the coupling current is induced and causes additional
coupling loss. Usually 3D modeling is needed to calculate the coupling loss but
it takes too much computing resource and time. In this paper, a numerical 2D
modeling by minimum electromagnetic entropy production (MEMEP) method is
developed to speed up the calculation. The presented MEMEP model shows good
accuracy and the capability to take the realistic resistance between tapes into
account for coupling loss calculation with a high number of mesh element, which
agrees to measurements.Thanks to the model, a systemic study of coupling loss
on amplitude-dependence, frequency-dependence, resistance-dependence, and
length-dependence, is presented and discussed. The results reveal the features
of coupling loss which is very helpful devices with multi-tape conductors, such
as the stator or rotor windings of motors. | 2001.02866v1 |
2020-05-22 | Aging Study on Resistive Plate Chambers of the CMS Muon Detector for HL-LHC | In the High Luminosity Large Hadron Collider (HL-LHC) program, during the
next years, the instantaneous luminosity will increase up to 5 $\times$
10$^{34}$ cm$^{-2}$ s$^{-1}$ which means a factor five higher than the nominal
LHC. In that period, the present CMS Resistive Plate Chambers (RPC) system will
be subjected to background rates higher than those for which the detectors have
been designed, which could affect the detector properties and induce aging
effects. To study whether the present RPC system can sustain the hard
background conditions during the HL-LHC running period, a dedicated longevity
test is ongoing at the CERN Gamma Irradiation Facility, where a few spare RPCs
are exposed to high gamma radiation for a long term period to mimic the HL-LHC
operational conditions. During the longevity test, the main detector parameters
are continuously monitored as a function of the integrated charge. Preliminary
results of the study, after having collected a sufficient amount of the
expected integrated charge at HL-LHC, will be presented. | 2005.11397v2 |
2020-06-03 | Suppression of Gate Screening on Edge Magnetoplasmons by Highly Resistive ZnO Gate | We investigate a way to suppress high-frequency coupling between a gate and
low-dimensional electron systems in the gigahertz range by measuring the
velocity of edge magnetoplasmons (EMPs) in InAs quantum Hall systems.We compare
the EMPvelocity in three samples with different electromagnetic
environments-one has a highly resistive zinc oxide (ZnO) top gate, another has
a normal metal (Ti/Au) top gate, and the other does not have a gate. The
measured EMP velocity in the ZnO gate sample is one order of magnitude larger
than that in the Ti/Au gate sample and almost the same as that in the ungated
sample. As is well known, the smaller velocity in the Ti/Au gate sample is due
to the screening of the electric field in EMPs. The suppression of the gate
screening effect in the ZnO gate sample allows us to measure the velocity of
unscreened EMPs while changing the electron density. It also offers a way to
avoid unwanted high-frequency coupling between quantum Hall edge channels and
gate electrodes. | 2006.01996v1 |
2020-06-05 | PLANS: Robust Program Learning from Neurally Inferred Specifications | Recent years have seen the rise of statistical program learning based on
neural models as an alternative to traditional rule-based systems for
programming by example. Rule-based approaches offer correctness guarantees in
an unsupervised way as they inherently capture logical rules, while neural
models are more realistically scalable to raw, high-dimensional input, and
provide resistance to noisy I/O specifications. We introduce PLANS (Program
LeArning from Neurally inferred Specifications), a hybrid model for program
synthesis from visual observations that gets the best of both worlds, relying
on (i) a neural architecture trained to extract abstract, high-level
information from each raw individual input (ii) a rule-based system using the
extracted information as I/O specifications to synthesize a program capturing
the different observations. In order to address the key challenge of making
PLANS resistant to noise in the network's output, we introduce a filtering
heuristic for I/O specifications based on selective classification techniques.
We obtain state-of-the-art performance at program synthesis from diverse
demonstration videos in the Karel and ViZDoom environments, while requiring no
ground-truth program for training. We make our implementation available at
github.com/rdang-nhu/PLANS. | 2006.03312v1 |
2020-07-15 | Model predictive control of resistive wall mode for ITER | Active feedback stabilization of the dominant resistive wall mode (RWM) for
an ITER H-mode scenario at high plasma pressure using infinite-horizon model
predictive control (MPC) is presented. The MPC approach is closely-related to
linear-quadratic-Gaussian (LQG) control, improving the performance in the
vicinity of constraints. The control-oriented model for MPC is obtained with
model reduction from a high-dimensional model produced by CarMa code. Due to
the limited time for on-line optimization, a suitable MPC formulation
considering only input (coil voltage) constraints is chosen, and the primal
fast gradient method is used for solving the associated quadratic programming
problem. The performance is evaluated in simulation in comparison to LQG
control. Sensitivity to noise, robustness to changes of unstable RWM dynamics,
and size of the domain of attraction of the initial conditions of the unstable
modes are examined. | 2007.07544v2 |
2021-03-02 | Numerical Qualification of Eco-Friendly Gas Mixtures for Avalanche-Mode Operation of Resistive Plate Chambers in INO-ICAL | Numerical qualification of an eco-friendly alternative gas mixture for
avalanche mode operation of Resistive Plate Chambers is the soul of this work.
To identify the gas mixture, a numerical model developed elsewhere by the
authors has been first established by comparing the simulated figure of merits
(efficiency and streamer probability) with the experimental data for the gas
mixture used in INO-ICAL. Then it has been used to simulate the same properties
of a gas mixture based on argon, carbon di-oxide and nitrogen, identified as
potential replacement by studying its different properties. Efficacy of this
eco-friendly gas mixture has been studied by comparing the simulated result
with the standard gas mixture used in INO-ICAL as well as with experimental
data of other eco-friendly hydrofluorocarbon (HFO1234ze) based potential
replacements. To increase the efficacy of the proposed gas mixture, studies of
the traditional way (addition of a little amount of SF$_6$) and an alternative
approach (exploring the option of high-end electronics) were carried out. | 2103.01906v2 |
2021-03-17 | Comprehensive study of out-of-plane transport properties in BaFe$_{2}$As$_{2}$: Three-dimensional electronic state and effect of chemical substitution | We investigated the out-of-plane transport properties of parent and
chemically substituted BaFe$_{2}$As$_{2}$ for various types of substitution.
Based on the studies of Hall coefficient and chemical-substitution effect, we
have clarified the origin for the unusual temperature dependence of
out-of-plane resistivity $\rho_c(T)$ in the high-temperature
paramagnetic-tetragonal phase. Electron (hole) carriers have an incoherent
(coherent) character, which is responsible for non-metallic (metallic)
$\rho_c(T)$. Although both of electron and hole contributions are almost
comparable, a slightly larger contribution comes from electrons at high
temperatures, while from holes at low temperatures, resulting in a maximum in
$\rho_c(T)$. In the low-temperature antiferromagnetic-orthorhombic phase, the
major effect of substitution is to increase the residual-resistivity component,
as in the case for the in-plane transport. In particular, Co atoms substituted
for Fe give rise to strong scattering with large $\mathit{ac}$ anisotropy. We
found that K substitution induces a non-metallic behavior in $\rho_c(T)$ at low
temperatures, which is likely due to a weakly localized nature along the
$c$-axis direction. | 2103.09700v1 |
2021-04-30 | Open-Source Memory Compiler for Automatic RRAM Generation and Verification | The lack of open-source memory compilers in academia typically causes
significant delays in research and design implementations. This paper presents
an open-source memory compiler that is directly integrated within the Cadence
Virtuoso environment using physical verification tools provided by Mentor
Graphics (Calibre). It facilitates the entire memory generation process from
netlist generation to layout implementation, and physical implementation
verification. To the best of our knowledge, this is the first open-source
memory compiler that has been developed specifically to automate Resistive
Random Access Memory (RRAM) generation. RRAM holds the promise of achieving
high speed, high density and non-volatility. A novel RRAM architecture,
additionally is proposed, and a number of generated RRAM arrays are evaluated
to identify their worst case control line parasitics and worst case settling
time across the memristors of their cells. The total capacitance of lines SEL,
N and P is 5.83 fF/cell, 3.31 fF/cell and 2.48 fF/cell respectively, while the
total calculated resistance for SEL is 1.28 Ohm/cell and 0.14 Ohm/cell for both
N and P lines. | 2104.14885v1 |
2021-08-19 | Monarch: A Durable Polymorphic Memory For Data Intensive Applications | 3D die stacking has often been proposed to build large-scale DRAM-based
caches. Unfortunately, the power and performance overheads of DRAM limit the
efficiency of high-bandwidth memories. Also, DRAM is facing serious scalability
challenges that make alternative technologies more appealing. This paper
examines Monarch, a resistive 3D stacked memory based on a novel reconfigurable
crosspoint array called XAM. The XAM array is capable of switching between
random access and content-addressable modes, which enables Monarch (i) to
better utilize the in-package bandwidth and (ii) to satisfy both the random
access memory and associative search requirements of various applications.
Moreover, the Monarch controller ensures a given target lifetime for the
resistive stack. Our simulation results on a set of parallel memory-intensive
applications indicate that Monarch outperforms an ideal DRAM caching by 1.21x
on average. For in-memory hash table and string matching workloads, Monarch
improves performance up to 12x over the conventional high bandwidth memories. | 2108.08497v1 |
2021-08-19 | Induced superconducting pairing in integer quantum Hall edge states | Indium Arsenide (InAs) near surface quantum wells (QWs) are promising for the
fabrication of semiconductor-superconductor heterostructures given that they
allow for a strong hybridization between the two-dimensional states in the
quantum well and the ones in the superconductor. In this work we present
results for InAs QWs in the quantum Hall regime placed in proximity of
superconducting NbTiN. We observe a negative downstream resistance with a
corresponding reduction of Hall (upstream) resistance, consistent with a very
high Andreev conversion. We analyze the experimental data using the
Landauer-B\"{u}ttiker formalism, generalized to allow for Andreev reflection
processes. We attribute the high efficiency of Andreev conversion in our
devices to the large transparency of the InAs/NbTiN interface and the
consequent strong hybridization of the QH edge modes with the states in the
superconductor. | 2108.08899v3 |
2021-12-26 | Self-discharge by streaming cosmic rays | A new nonthermal phenomenon caused by streaming cosmic rays (CRs) in the
universe is proposed. The streaming CRs drive the return current of thermal
electrons to compensate for the CR current. Then, electric fields are induced
by the resistivity of the return current. It is shown that the resistive
electric fields can accelerate secondary electrons generated by the streaming
CRs. This is the self-discharge by streaming CRs. In this work, the
self-discharge condition and the condition for runaway acceleration of
secondary electrons are presented. The self-discharge makes high-energy
secondary electrons, resulting in enhancements of ionization and nonthermal
emission including K$\alpha$ emission line of neutral irons. After the
self-discharge, the return current of thermal electrons is replaced by the
electric current of secondary electrons. Since some magnetic field generations
and amplifications are driven by the return current of thermal electrons, the
self-discharge can significantly influence them. | 2112.13395v2 |
2022-01-03 | Performance of a prototype bakelite RPC at GIF++ using self-triggered electronics for the CBM Experiment at FAIR | The Muon Chamber (MuCh) is a sub-system of the Compressed Baryonic Matter
(CBM) experiment for the detection of low-mass-vector mesons produced in high
energy heavy-ion collisions at beam energies ranging from 2 AGeV to 11 AGeV and
decaying in the di-muon channel. MuCh consists of a segmented absorber and four
detector triplet stations sandwiched between the absorber segments. At the 3rd
and 4th stations of MuCh, Resistive Plate Chambers (RPCs) have been conceived
for muon tracking. We have tested the performance of a low resistivity bakelite
RPC prototype equipped with self-triggered front end electronics (MuCh-XYTER)
for the CBM Muon Chamber. A systematic study on the muon detection efficiency
and time resolution has been carried out in a high-rate photon background at
the Gamma Irradiation Facility (GIF++) at CERN. The details of the measurement
setup and the results are presented here. | 2201.00661v1 |
2022-01-21 | Multidimensional minimum-work control of a 2D Ising model | A system's configurational state can be manipulated using dynamic variation
of control parameters, such as temperature, pressure, or magnetic field; for
finite-duration driving, excess work is required above the equilibrium
free-energy change. Minimum-work protocols in multidimensional
control-parameter space have potential to significantly reduce work relative to
one-dimensional control. By numerically minimizing a linear-response
approximation to the excess work, we design protocols in control-parameter
spaces of a 2D Ising model that efficiently drive the system from the all-down
to all-up configuration. We find that such designed multidimensional protocols
take advantage of more flexible control to avoid control-parameter regions of
high system resistance, heterogeneously input and extract work to make use of
system relaxation, and flatten the energy landscape, making accessible many
configurations that would otherwise have prohibitively high energy and thus
decreasing spin correlations. Relative to one-dimensional protocols, this
speeds up the rate-limiting spin-inversion reaction, thereby keeping the system
significantly closer to equilibrium for a wide range of protocol durations, and
significantly reducing resistance and hence work. | 2201.08925v2 |
2022-03-14 | Planckian Dissipation and non-Ginzburg-Landau Type Upper Critical Field in Bi2201 | Resistivity and Hall effect measurements have been carried out on a
micro-fabricated bridge of Bi2201 single crystal at low temperatures down to
0.4 K under high magnetic fields. When superconductivity is crashed by a high
magnetic field, the recovered "normal state" resistivity still shows a linear
temperature dependence in low temperature region. Combining with the effective
mass and the charge carrier density, we get a linear scattering rate $1/\tau =
\alpha k_{B} T/\hbar$ with $0.77<\alpha<1.16$, which gives a strong evidence of
the Planckian dissipation. Furthermore, our results reveal a new type of
temperature dependence of upper critical field,
$H_{c2}(T)=H^*\sqrt{(1-t)/(t+0.154)}$, which is totally different from the
expectation of the Ginzburg-Landau theory, and suggests uncondensed Cooper
pairs above $H_{c2}(T)$ line. | 2203.06879v3 |
2022-04-04 | Optimisation of Operating High Voltage of the large area Resistive Plate Chamber for ICAL experiment | The Resistive Plate Chamber is a widely used detector in high energy physics.
The operating potential of this chamber is determined by the optimisation of
the efficiency and noise rate of the device. This optimisation is based on the
assumption that the performance of the device over the whole surface area is
uniform. The INO-ICAL experiment is going to use $\sim$ 30000 RPC of size
$\sim$2\,m$\times$2\,m. All the RPC will have to pass a minimum quality
assurance criteria, but may not be able to maintain a good uniformity over the
whole surface area, particularly for the whole running period of about twenty
years. This paper describes the choice of the optimum operating HV for an RPC
of non-uniform response. | 2204.01251v1 |
2022-04-05 | An optical transition-edge sensor with high energy resolution | Optical transition-edge sensors have shown energy resolution for resolving
the number of incident photons at the telecommunication wavelength. Higher
energy resolution is required for biological imaging and microscope
spectroscopy. In this paper, we report on a Au/Ti (10/20 nm) bilayer TES that
showed high energy resolution. This was achieved by lowering the critical
temperature Tc to 115 mK and the resultant energy resolution was 67 meV full
width at half maximum (FWHM) at 0.8 eV. When Tc was lowered to 115 mK, the
theoretical resolution would scaled up to 30 meV FWHM, considering that the
typical energy resolution of optical TESs is 150 meV and Tc is 300 mK. To
investigate the gap between the theoretical expectation (30 meV) and the
measured value (67 meV), we measured its complex impedance and current noise.
We found excess Johnson noise in the TES and an excess Johnson term M was 1.5
at a bias point where the resistance was 10% of normal resistance. For
reference, the TES was compared with a TES showing typical energy resolution
(156 meV FWHM). We will discuss what improved the energy resolution and what
might have been the limiting factor on it. | 2204.01903v1 |
2022-05-05 | Precursor superconducting effects in the optimally doped YBa$_2$Cu$_3$O$_{7-δ}$ superconductor: the confrontation between superconducting fluctuations and percolative effects revisited | The confrontation between the superconducting fluctuations and percolation
effects as the origin of the in-plane paraconductivity in cuprate
superconductors was earlier addressed at a quantitative level in the case of
the optimally doped YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO) compound. Using in-plane
resistivity data from a high-quality YBCO thin film, we will extend these
analyses to high reduced temperatures, in the case of the
Gaussian-Ginzburg-Landau (GGL) approach for the conventional superconducting
fluctuations, by considering the total energy cutoff. These data will also be
analysed in terms of the mean field-approach of the effective-medium theory, to
probe if emergent percolative effects may account for the resistivity rounding
above $T_c$. Our analyses confirm earlier conclusions: the measured
paraconductivity cannot be explained in terms of emergent percolation
processes, but it may be accounted for in terms of the GGL approach. These
results also call into question alternative scenarios, including a recent
proposal derived from emergent percolative effects. | 2205.02812v1 |
2022-08-31 | Ferroelectric FET-based strong physical unclonable function: a low-power, high-reliable and reconfigurable solution for Internet-of-Things security | Hardware security has been a key concern in modern information technologies.
Especially, as the number of Internet-of-Things (IoT) devices grows rapidly, to
protect the device security with low-cost security primitives becomes
essential, among which Physical Unclonable Function (PUF) is a widely-used
solution. In this paper, we propose the first FeFET-based strong PUF exploiting
the cycle-to-cycle (C2C) variation of FeFETs as the entropy source. Based on
the experimental measurements, the proposed PUF shows satisfying performance
including high uniformity, uniqueness, reconfigurability and reliability. To
resist machine-learning attack, XOR structure was introduced, and simulations
show that our proposed PUF has similar resistance to existing attack models
with traditional arbiter PUFs. Furthermore, our design is shown to be
power-efficient, and highly robust to write voltage, temperature and device
size, which makes it a competitive security solution for Internet-of-Things
edge devices. | 2208.14678v1 |
2023-04-28 | The Volume of Healthy Red Blood Cells is Optimal for Advective Oxygen Transport in Arterioles | Red blood cells (RBCs) are vital for transporting oxygen from the lungs to
the body's tissues through the intricate circulatory system. They achieve this
by binding and releasing oxygen molecules to the abundant hemoglobin within
their cytosol. The volume of RBCs affects the amount of oxygen they can carry,
yet whether this volume is optimal for transporting oxygen through the
circulatory system remains an open question. This study explores, through
high-fidelity numerical simulations, the impact of RBC volume on advectve
oxygen transport efficiency through arterioles which form the area of greatest
flow resistance in the circulatory system. The results show that, strikingly,
RBCs with volumes similar to those found in vivo are most efficient to
transport oxygen through arterioles. The flow resistance is related to the
cell-free layer thickness, which is influenced by the shape and the motion of
the RBCs: at low volumes RBCs deform and fold while at high volumes RBCs
collide and follow more diffuse trajectories. In contrast, RBCs with a healthy
volume maximize the cell-free layer thickness, resulting in a more efficient
advectve transport of oxygen. | 2305.02197v2 |
2023-06-04 | Observations of the Current Sheet Heating in X-ray during a Solar Flare | In the solar corona, magnetic reconnection occurs due to the finite
resistivity of the plasma. At the same time, resistivity leads to ohmic
heating. Therefore, the reconnecting current sheet should heat the surrounding
plasma. This paper presents experimental evidence of such plasma heating caused
by magnetic reconnection. We observed the effect during a C1.4 solar flare on
16 February 2003 at the active region NOAA 10278, near the solar limb. Thanks
to such a location, we successfully identified all the principal elements of
the flare: the flare arcade, the fluxrope, and, most importantly, the presumed
position of the current sheet. By analyzing the monochromatic X-ray images of
the Sun obtained by the CORONAS-F/SPIRIT instrument in the Mg XII 8.42 A
spectral line, we detected a high-temperature ($T \geq$ 4 MK) emission at the
predicted location of the current sheet. The high-temperature emission appeared
during the CME impulsive acceleration phase. We believe that this additionally
confirms that the plasma heating around the current sheet and magnetic
reconnection inside the current sheet are strongly connected. | 2306.02355v1 |
2023-10-18 | Thermo-electric Transport of Dyonic Gubser-Rocha Black Holes | We study the thermo-electric transport coefficients of an extended version of
the Gubser-Rocha model. After reviewing the two relaxation time model from
holography and studying the effect of the magnetic field on thermo-electric
transports from hydrodynamic theory, we present a new dilatonic dyonic
asymptotically AdS black hole solution. Notice that S-duality plays an
important role in finding the analytic solution with the magnetic field. Using
the AdS/CMT dictionary, we analyze the electric and thermo-electric transport
properties of the dual field theory. The resistivity exhibits T-linearity in
the low-temperature regime. However, in the strong momentum relaxation and a
strong magnetic field limit, the resistivitiy shows explicit deviation from the
linear-in-T resistivity. The Hall angle is linear-in-T for both the
low-temperature regime and the high-temperature regime for fixed momentum
dissipation strength. The Nernst signal is a bell-shaped function in terms of
the magnetic field even when the momentum relaxation is strong. Finally, we
discuss the possibility of getting a semi-realistic strange metal description
from our model. | 2310.12067v1 |
2024-01-24 | Heterogeneously Integrated Laser on Silicon with Non-Volatile Wavelength Tuning | The von-Neumann bottleneck has constrained computing systems from efficiently
operating on the increasingly large demand in data from networks and devices.
Silicon (Si) photonics offers a powerful solution for this issue by providing a
platform for high-bandwidth, energy-efficient interconnects. Furthermore,
memristors have emerged as a fundamental building block for non-volatile data
storage and novel computing architectures with powerful in-memory processing
capabilities. In this paper, we integrate an Al2O3 memristor into a
heterogeneous Si quantum dot microring laser to demonstrate the first laser
with non-volatile optical memory. The memristor alters the effective optical
modal index of the microring laser cavity by the plasma dispersion effect in
the high resistance state (HRS) or Joule heating in the low resistance state
(LRS), subsequently controlling the output wavelength of the laser in a
non-volatile manner. This device enables a novel pathway for future
optoelectronic neuromorphic computers and optical memory chips. | 2401.13757v1 |
2024-03-29 | Deepfake Sentry: Harnessing Ensemble Intelligence for Resilient Detection and Generalisation | Recent advancements in Generative Adversarial Networks (GANs) have enabled
photorealistic image generation with high quality. However, the malicious use
of such generated media has raised concerns regarding visual misinformation.
Although deepfake detection research has demonstrated high accuracy, it is
vulnerable to advances in generation techniques and adversarial iterations on
detection countermeasures. To address this, we propose a proactive and
sustainable deepfake training augmentation solution that introduces artificial
fingerprints into models. We achieve this by employing an ensemble learning
approach that incorporates a pool of autoencoders that mimic the effect of the
artefacts introduced by the deepfake generator models. Experiments on three
datasets reveal that our proposed ensemble autoencoder-based data augmentation
learning approach offers improvements in terms of generalisation, resistance
against basic data perturbations such as noise, blurring, sharpness
enhancement, and affine transforms, resilience to commonly used lossy
compression algorithms such as JPEG, and enhanced resistance against
adversarial attacks. | 2404.00114v1 |
2011-03-05 | Physics and measurements of magnetic materials | Magnetic materials, both hard and soft, are used extensively in several
components of particle accelerators. Magnetically soft iron-nickel alloys are
used as shields for the vacuum chambers of accelerator injection and extraction
septa; Fe-based material is widely employed for cores of accelerator and
experiment magnets; soft spinel ferrites are used in collimators to damp
trapped modes; innovative materials such as amorphous or nanocrystalline core
materials are envisaged in transformers for high-frequency polyphase resonant
convertors for application to the International Linear Collider (ILC). In the
field of fusion, for induction cores of the linac of heavy-ion inertial fusion
energy accelerators, based on induction accelerators requiring some 107 kg of
magnetic materials, nanocrystalline materials would show the best performance
in terms of core losses for magnetization rates as high as 105 T/s to 107 T/s.
After a review of the magnetic properties of materials and the different types
of magnetic behaviour, this paper deals with metallurgical aspects of
magnetism. The influence of the metallurgy and metalworking processes of
materials on their microstructure and magnetic properties is studied for
different categories of soft magnetic materials relevant for accelerator
technology. Their metallurgy is extensively treated. Innovative materials such
as iron powder core materials, amorphous and nanocrystalline materials are also
studied. A section considers the measurement, both destructive and
non-destructive, of magnetic properties. Finally, a section discusses magnetic
lag effects. | 1103.1069v1 |
2021-03-14 | JAMIP: an artificial-intelligence aided data-driven infrastructure for computational materials informatics | Materials informatics has emerged as a promisingly new paradigm for
accelerating materials discovery and design. It exploits the intelligent power
of machine learning methods in massive materials data from experiments or
simulations to seek for new materials, functionality, principles, etc.
Developing specialized facility to generate, collect, manage, learn and mine
large-scale materials data is crucial to materials informatics. We herein
developed an artificial-intelligence-aided data-driven infrastructure named
Jilin Artificial-intelligence aided Materials-design Integrated Package
(JAMIP), which is an open-source Python framework to meet the research
requirements of computational materials informatics. It is integrated by
materials production factory, high-throughput first-principles calculations
engine, automatic tasks submission and monitoring progress, data extraction,
management and storage system, and artificial intelligence machine learning
based data mining functions. We have integrated specific features such as
inorganic crystal structure prototype database to facilitate high-throughput
calculations and essential modules associated with machine learning studies of
functional materials. We demonstrated how our developed code is useful in
exploring materials informatics of optoelectronic semiconductors by taking
halide perovskites as typical case. By obeying the principles of automation,
extensibility, reliability and intelligence, the JAMIP code is a promisingly
powerful tool contributing to the fast-growing field of computational materials
informatics. | 2103.07957v1 |
2010-07-08 | A Model of the Number of Antibiotic Resistant Bacteria in Rivers | The large reservoir of antibiotic resistant bacteria in raw and treated water
supplies is a matter of public health concern. Currently, the National
Antimicrobial Resistance Monitoring Systems, a collaborative effort of the
Centers for Disease Control, the US Department of Agriculture, and the US Food
and Drug Administration, does not monitor antimicrobial resistance in surface
waters. Given the serious nature of antibiotic resistance in clinical settings,
and the likelihood that antibiotic resistant bacteria can be transmitted to
humans from large environmental reservoirs via drinking water, explanations for
the distribution of antibiotic resistant bacteria and tools for studying this
distribution must be found. Here we focus on mathematical modeling of
cultivable bacteria in a river, which will be used to study the distribution of
antibiotic resistant bacteria in the environment. We consider both antibiotic
resistant and non-antibiotic resistant bacteria in the model, and, taking into
account the strong correlation between land use and antibiotic resistant
bacteria in rivers, we include a function for the influx of bacteria into the
river from the shore. We simulate the model for two different time scales and
show that if there is too many bacteria from the land entering the river, the
river entirely fills with antibiotic resistant bacteria, while less frequent
influxes allows time for the bacteria to lose the antibiotic resistant gene.
This mathematically verifies that reduction in antibiotic use near the banks of
rivers, will reduce the counts of antibiotic resistant bacteria in rivers. | 1007.1383v1 |
2024-01-02 | A comparative study of resistivity models for simulations of magnetic reconnection in the solar atmosphere. II. Plasmoid formation | Plasmoid-mediated reconnection plays a fundamental role in different solar
atmospheric phenomena. Numerical reproduction of this process is therefore
essential for developing robust solar models. Our goal is to assess
plasmoid-mediated reconnection across various numerical resistivity models in
order to investigate how plasmoid numbers and reconnection rates depend on the
Lundquist number. We used the Bifrost code to drive magnetic reconnection in a
2D coronal fan-spine topology, carrying out a parametric study of several
experiments with different numerical resolution and resistivity models. We
employed three anomalous resistivity models: (1) the original hyper-diffusion
from Bifrost, (2) a resistivity proportional to current density, and (3) a
resistivity quadratically proportional to electron drift velocity. For
comparisons, experiments with uniform resistivity were also run.
Plasmoid-mediated reconnection is obtained in most of the experiments. With
uniform resistivity, increasing the resolution reveals higher plasmoid
frequency with weaker scaling to the Lundquist number, obtaining 7.9-12
plasmoids per minute for $S_L\in[1.8 \times 10^4, 2.6\times 10^5]$ with a
scaling of $S_L^{0.210}$ in the highest-resolution resistivity cases,
transcending into Petschek reconnection in the high-$S_L$ limit and
Sweet-Parker reconnection in the low-$S_L$ limit. Anomalous resistivity leads
to similar results even with lower resolution. The drift-velocity-dependent
resistivity excellently reproduces Petschek reconnection for any Lundquist
number, and similar results are seen with resistivity proportional to
current-density. Among the different resistivity models applied on the given
numerical resolution, the hyper-diffusion model reproduced plasmoid
characteristics in closest resemblance to those obtained with uniform
resistivity at a significantly higher resolution. | 2401.01177v1 |
2007-11-20 | Induction of nuclear fission by high-voltage application | In nuclear power generation, fissile materials are mainly used. For example,
$U^{235}$ is fissile and therefore quite essential for use of nuclear energy.
However, the material $U^{235}$ has very small natural abundance less than 1 %.
We should seek possibility of utilizing fissionable materials such as $U^{238}$
because natural abundance of such fissionable materials is generally much
larger than fissile ones. In this paper, we show that thermal neutrons with
vanishing kinetic energy can induce nuclear fission when high voltage is
applied to fissionable materials. To obtain this result, we use the liquid-drop
model for nuclei. Finally, we propose how fissionable materials can be
utilized. | 0711.3153v1 |
2020-06-17 | Simulation of Particle-Material Interactions | This paper gives an overview of the particle transport theory essentials, the
basics of particle-material interaction simulation, physical quantities needed
to simulate particle transport and interactions in materials, Monte Carlo
simulation flow, response of additive detectors, statistical weights and other
techniques to minimize statistical errors. Effects in materials under
irradiation, materials response related to component lifetime and performance
are considered with a focus on high-energy and high-power accelerator
applications. Implementation of simulation of particle-material interactions in
the modern Monte Carlo codes along with the code s main features and results of
recent benchmarking are described. | 2006.09866v1 |
2003-03-04 | Accretion of low angular momentum material onto black holes: 2D magnetohydrodynamical case | We report on the second phase of our study of slightly rotating accretion
flows onto black holes. We consider magnetohydrodynamical (MHD) accretion flows
with a spherically symmetric density distribution at the outer boundary, but
with spherical symmetry broken by the introduction of a small,
latitude-dependent angular momentum and a weak radial magnetic field. We study
accretion flows by means of numerical 2D, axisymmetric, MHD simulations with
and without resistive heating. Our main result is that the properties of the
accretion flow depend mostly on an equatorial accretion torus which is made of
the material that has too much angular momentum to be accreted directly. The
torus accretes, however, because of the transport of angular momentum due to
the magnetorotational instability (MRI). Initially, accretion is dominated by
the polar funnel, as in the hydrodynamic inviscid case, where material has zero
or very low angular momentum. At the later phase of the evolution, the torus
thickens towards the poles and develops a corona or an outflow or both.
Consequently, the mass accretion through the funnel is stopped. The accretion
of rotating gas through the torus is significantly reduced compared to the
accretion of non-rotating gas (i.e., the Bondi rate). It is also much smaller
than the accretion rate in the inviscid, weakly rotating case.Our results do
not change if we switch on or off resistive heating. Overall our simulations
are very similar to those presented by Stone, Pringle, Hawley and Balbus
despite different initial and outer boundary conditions. Thus, we confirm that
MRI is very robust and controls the nature of radiatively inefficient accretion
flows. | 0303093v1 |
2002-05-17 | A systematic study of four series of electron-doped rare earth manganates, LnxCa1-xMnO3 (Ln=La, Nd, Gd and Y) over the x=0.02-0.25 composition range | Electrical and magnetic properties of four series of manganates LnxCa1-xMnO3
(Ln=La, Nd, Gd and Y) have been studied in the electron doped regime
(x=0.02-0.25) in order to investigate the various inter-dependent phenomena
such as ferromagnetism, phase separation and charge ordering. The general
behavior of all the four series of manganates is similar, with some of the
properties showing dependence on the average radius of the A-site cations, <rA>
and cation size disorder. Thus, all the compositions show increase in
magnetization at 100-120 K (TM) for x<xmax, the magnetization increasing with
increasing x. The value of xmax increases with decreasing <rA>, probably due to
the increased phase separation induced by site disorder. This is also reflected
in the larger width of the hysteresis loops at T<TM for small x or <rA>. In
this regime, the electrical resistivity decreases with increasing x, but
remains low and nearly constant T>TM. The percolative nature of the conduction
mechanism at T<TM is substantiated by the fit of the conductivity data to the
scaling law, s \mu |xc-x|p where p is in the 2-4 range. When x>xmax, the
materials become antiferromagnetic and charge-ordered at a temperature TCA,
accompanied by a marked increase in resistivity. The value of TCA increases
with increase in <rA> and x (upto x=0.3). Thus, all the four series of
manganates are characterized by a phase-separated regime between x=0.02 and
0.1-0.15 and an antiferromagnetic charge-ordered regime at x>0.1-0.15. | 0205370v2 |
2017-10-25 | NaSn2As2: An Exfoliatable Layered van der Waals Zintl Phase | The discovery of new families of exfoliatable 2D crystals that have diverse
sets of electronic, optical, and spin-orbit coupling properties, enables the
realization of unique physical phenomena in these few-atom thick building
blocks and in proximity to other materials. Herein, using NaSn2As2 as a model
system, we demonstrate that layered Zintl phases having the stoichiometry
ATt2Pn2 (A = Group 1 or 2 element, Tt = Group 14 tetrel element and Pn = Group
15 pnictogen element) and feature networks separated by van der Waals gaps can
be readily exfoliated with both mechanical and liquid-phase methods. We
identified the symmetries of the Raman active modes of the bulk crystals via
polarized Raman spectroscopy. The bulk and mechanically exfoliated NaSn2As2
samples are resistant towards oxidation, with only the top surface oxidizing in
ambient conditions over a couple of days, while the liquid-exfoliated samples
oxidize much more quickly in ambient conditions. Employing angle-resolved
photoemission spectroscopy (ARPES), density functional theory (DFT), and
transport on bulk and exfoliated samples, we show that NaSn2As2 is a highly
conducting 2D semimetal, with resistivities on the order of 10-6 {\Omega} m.
Due to peculiarities in the band structure, the dominating p-type carriers at
low temperature are nearly compensated by the opening of n-type conduction
channels as temperature increases. This work further expands the family of
exfoliatable 2D materials to layered van der Waals Zintl phases, opening up
opportunities in electronics and spintronics. | 1710.09059v1 |
2017-12-06 | Interfacial Strain Effects on Lithium Diffusion Pathways in the Spinel Solid Electrolyte Li-Doped MgAl$_2$O$_4$ | (Li,Al)-co-doped magnesium spinel (Li$_x$Mg$_{1-2x}$Al$_{2+x}$O$_4$) is a
solid lithium-ion electrolyte with potential use in all-solid-state lithium-ion
batteries. Interfaces with spinel electrodes, such as Li$_y$Mn$_2$O$_4$ and
Li$_{4+3z}$Ti$_5$O$_{12}$, may be lattice-matched, with potentially low
interfacial resistances. Small lattice parameter differences across a
lattice-matched interface are unavoidable, causing residual epitaxial strain.
This strain potentially modifies lithium diffusion near the interface,
contributing to interfacial resistance. Here we report a density functional
theory study of strain effects on lithium diffusion pathways for
(Li,Al)-co-doped magnesium spinel, for $x_\mathrm{Li} = 0.25$ and
$x_\mathrm{Li} = 0.5$. We have calculated diffusion profiles for the
un-strained materials, and for isotropic and biaxial tensile strains of up to
6%, corresponding to {100} epitaxial interfaces with Li$_y$Mn$_2$O$_4$ and
Li$_{4+3z}$Ti$_5$O$_{12}$. We find that isotropic tensile strain reduces
lithium diffusion barriers by as much as 0.32 eV, with typical barriers reduced
by ~0.1 eV. This effect is associated with increased volumes of transitional
octahedral sites, and broadly follows local electrostatic potentials. For
biaxial (epitaxial) strain changes in octahedral site volumes and in lithium
diffusion barriers are much smaller than under isotropic strain. Typical
barriers are reduced by only ~ 0.05 eV. Individual effects, however, depend on
the pathway considered and the relative strain orientation. These results
predict that isotropic strain strongly affects ionic conductivities in
(Li,Al)-co-doped magnesium spinel electrolytes, and that tensile strain is a
potential route to enhanced lithium transport. For a lattice-matched interface
with candidate spinel-structured electrodes epitaxial strain has a small, but
complex, effect on lithium diffusion barriers. | 1712.02156v3 |
2022-01-20 | Pseudo-hydrodynamic flow of quasiparticles in semimetal WTe2 at room temperature | Recently, much interest has emerged in fluid-like electric charge transport
in various solid-state systems. The hydrodynamic behavior of the electronic
fluid reveals itself as a decrease of the electrical resistance with increasing
temperature (the Gurzhi effect) in narrow conducting channels, polynomial
scaling of the resistance as a function of the channel width, substantial
violation of the Wiedemann-Franz law supported by the emergence of the
Poiseuille flow. Similarly to whirlpools in flowing water, the viscous
electronic flow generates vortices, resulting in abnormal sign-changing
electrical response driven by the backflow of electrical current.
Experimentally, the presence of the hydrodynamic vortices was observed in
low-temperature graphene as a negative voltage drop near the current-injecting
contacts. However, the question of whether the long-ranged sign-changing
electrical response can be produced by a mechanism other than hydrodynamics has
not been addressed so far. Here we use polarization-sensitive laser microscopy
to demonstrate the emergence of visually similar abnormal sign-alternating
patterns in charge density in multilayer tungsten ditelluride at room
temperature where this material does not exhibit true electronic hydrodynamics.
We argue that this pseudo-hydrodynamic behavior appears due to a subtle
interplay between the diffusive transport of electrons and holes. In
particular, the sign-alternating charge accumulation in WTe2 is supported by
the unexpected backflow of compressible neutral electron-hole current, which
creates charge-neutral whirlpools in the bulk of this nearly compensated
semimetal. We demonstrate that the exceptionally large spatial size of the
charge domains is sustained by the long recombination time of electron-hole
pairs. | 2201.08331v1 |
2022-08-19 | Electron transport properties of a narrow-bandgap semiconductor Bi$_2$O$_2$Te nanosheet | A thin, narrow-bandgap semiconductor Bi$_2$O$_2$Te nanosheet is obtained via
mechanical exfoliation and a Hall-bar device is fabricated from it on a heavily
doped Si/SiO$_2$ substrate and studied at low temperatures. Gate transfer
characteristic measurements show that the transport carriers in the nanosheet
are of $n$-type. The carrier density, mobility, and mean free path in the
nanosheet are determined by measurements of the Hall resistance and the
longitudinal resistance of the Hall-bar device and it is found that the
electron transport in the nanosheet is in a quasi-two-dimensional (2D),
strongly disordered regime. Magnetotransport measurements for the device at
magnetic fields applied perpendicular to the nanosheet plane show dominantly
weak antilocalization (WAL) characteristics at low fields and a linear
magnetoresistance (LMR) behavior at large fields. We attribute the WAL
characteristics to strong spin-orbit interaction (SOI) and the LMR to the
classical origin of strong disorder in the nanosheet. Low-field
magnetoconductivity measurements are also performed and are analyzed based on
the multi-channel Hikami-Larkin-Nagaoka theory with the LMR correction being
taken into account. The phase coherence length, spin relaxation length,
effective 2D conduction channel number and coefficient in the linear term due
to the LMR in the nanosheet are extracted. It is found that the spin relaxation
length in the Bi$_2$O$_2$Te nanosheet is several times smaller than it in its
counterpart Bi$_2$O$_2$Se nanosheet and thus an ultra-strong SOI is present in
the Bi$_2$O$_2$Te nanosheet. Our results reported in this study would greatly
encourage further studies and applications of this emerging narrow-bandgap
semiconductor 2D material. | 2208.09361v1 |
2022-10-20 | Seebeck coefficient in a nickelate superconductor: electronic dispersion in the strange metal phase | Superconducting nickelates are a new family of materials that combine
strongly-correlated magnetism with unconventional superconductivity. While
comparisons with the superconducting cuprates are natural, very little is known
about the metallic state of the nickelates, making these comparisons difficult.
We probe the electronic dispersion of thin-film superconducting 5-layer ($n=5$)
and metallic 3-layer ($n=3$) nickelates by measuring the Seebeck coefficient,
$S$. We find a temperature independent and negative $S/T$ for both the $n=5$
nickelate, with strange metal resistivity, and the $n=3$ compound, with more
conventional Fermi liquid resistivity. These results are in stark contrast with
the strongly temperature-dependent $S/T$ measured at similar electron filling
in the cuprate La$_{1.36}$Nd$_{0.4}$Sr$_{0.24}$CuO$_4$. We reproduce the
temperature dependence, sign, and amplitude of $S/T$ in the nickelates using
Boltzmann transport theory combined with the electronic structure calculated
from density functional theory. This demonstrates that the electronic structure
obtained from first-principles calculations is a good starting point for
calculating the transport properties of superconducting nickelates, and
suggests that, despite indications of strong electronic correlations, there are
well-defined quasiparticles in the metallic state of this family of materials.
Finally, we explain the differences in the Seebeck coefficient between
nickelates and cuprates as originating in strong dissimilarities in impurity
concentrations. Beyond establishing a baseline understanding of how the
electronic structure relates to transport coefficients in these new materials,
this work demonstrates the power of the semi-classical approach to
quantitatively describe transport measurements, even in the strange-metallic
state. | 2210.10987v2 |
2023-04-19 | Realization of Z$_2$ Topological Metal in Single-Crystalline Nickel Deficient NiV$_2$Se$_4$ | Temperature-dependent electronic and magnetic properties are reported for a
Z2 topological metal single-crystalline nickel-deficient NiV$_2$Se$_4$. It is
found to crystallize in the monoclinic Cr3S4 structure type with space group
I2=m. From single-crystal x-ray diffraction, we find that there are vacancies
on the Ni site, resulting in the composition Ni0:85V2Se4 in agreement with our
electron-probe microanalysis. The electrical resistivity shows metallic
behavior with a broad anomaly around 150{200 K that is also observed in the
heat capacity data. This anomaly indicates a change of state of the material
below 150 K. We believe that this anomaly could be due to spin fluctuations or
charge-density-wave (CDW) fluctuations, where the lack of long-range order is
caused by vacancies at the Ni site of Ni0:85V2Se4. Although we fail to observe
any structural distortion in this crystal down to 1.5 K, its electronic and
thermal properties are anomalous. The observation of non-linear temperature
dependence of resistivity as well as an enhanced value of the Sommerfeld
coefficient = 104.0(1) mJ/molK2 suggests strong electron-electron correlations
in this material. The first-principles calculations performed for
NiV$_2$Se$_4$, which are also applicable to Ni0:85V2Se4, classify this material
as a topological metal with Z2 = (1; 110) and coexisting electron and hole
pockets at the Fermi level. The phonon spectrum lacks any soft phonon mode,
consistent with the absence of periodic lattice distortion in the present
experiments. | 2304.09357v1 |
2024-05-17 | Unconventional Unidirectional Magnetoresistance in vdW Heterostructures | Electrical readout of magnetic states is a key to realize novel spintronics
devices for efficient computing and data storage. Unidirectional
magnetoresistance (UMR) in bilayer systems, consisting of a spin source
material and a magnetic layer, refers to a change in the longitudinal
resistance upon the reversal of magnetization, which typically originates from
the interaction of spin-current and magnetization at the interface. Because of
UMR s linear dependence on applied charge current and magnetization, it can be
used to electrically read the magnetization state. However, in conventional
spin source materials, the spin polarization of an electric field induced spin
current is restricted to be in the film plane and hence the ensuing UMR can
only respond to the in plane component of the magnetization. On the other hand,
magnets with perpendicular magnetic anisotropy (PMA) are highly desired for
magnetic memory and spin-logic devices, while the electrical read out of PMA
magnets through UMR is critically missing. Here, we report the discovery of an
unconventional UMR in bilayer heterostructures of a topological semimetal
(WTe2) and a PMA ferromagnetic insulator (Cr2Ge2Te6, CGT), which allows to
electrically read the up and down magnetic states of the CGT layer by measuring
the longitudinal resistance. Our theoretical calculations based on a tight
binding model show that the unconventional UMR originates from the interplay of
crystal symmetry breaking in WTe2 and magnetic exchange interaction across the
WTe2 and CGT interface. Combining with the ability of WTe2 to obtain magnetic
field free switching of the PMA magnets, our discoveries open an exciting
pathway to achieve two terminal magnetic memory devices that operate solely on
the spin orbit torque and UMR, which is critical for developing next-generation
non volatile and low power consumption data storage technologies. | 2405.10889v1 |
2024-05-21 | Spin-polarized p-wave superconductivity in the kagome material RbV$_3$Sb$_5$ | The study of kagome materials has attracted much attention in the past few
years due to the presence of many electron-electron interaction-driven phases
in a single material.In this work, we report the discovery of intrinsic
spin-polarized p-wave superconductivity in the thin-flake kagome material
RbV$_3$Sb$_5$. Firstly, when an in-plane magnetic field is swept in opposite
directions, we observe a unique form of hysteresis in magnetoresistance which
is different from the hysteresis induced by extrinsic mechanisms such as
flux-trapping or superheating and supercooling effects. The unconventional
hysteresis indicates the emergence of an intrinsic time-reversal
symmetry-breaking superconducting phase. Strikingly, at a fixed magnetic field,
the finite-resistance state can be quenched to the zero-resistance state by
applying a large current. Secondly, at temperatures around 400 mK, the
re-entrance of superconductivity occurs during an in-plane field-sweeping
process with a fixed sweeping direction. This kind of re-entrance is asymmetric
about the zero field axis and observed in all field directions for a fixed
current direction, which is different from the re-entrance observed in
conventional superconductors. Moreover, the angle-dependent in-plane critical
field measurements reveal a two-fold symmetry that deviates from the original,
centrosymmetric D$_{6h}$ point group symmetry of the crystal. These findings
put very strong constraints on the possible superconducting pairing symmetry of
RbV$_3$Sb$_5$. We point out that the pairing symmetry, which is consistent with
the crystal symmetry and all the observed novel properties, is a time-reversal
symmetry-breaking, p-wave pairing with net spin polarization. Importantly, this
p-wave pairing gives rise to a nodal topological superconducting state with
Majorana flat bands on the sample edges. | 2405.12592v1 |
2003-10-07 | Study of coupling loss on bi-columnar BSCCO/Ag tapes by a.c. susceptibility measurements | Coupling losses were studied in composite tapes containing superconducting
material in the form of two separate stacks of densely packed filaments
embedded in a metallic matrix of Ag or Ag alloy. This kind of sample geometry
is quite favorable for studying the coupling currents and in particular the
role of superconducting bridges between filaments. By using a.c. susceptibility
technique, the electromagnetic losses as function of a.c. magnetic field
amplitude and frequency were measured at the temperature T = 77 K for two tapes
with different matrix composition. The length of samples was varied by
subsequent cutting in order to investigate its influence on the dynamics of
magnetic flux penetration. The geometrical factor $\chi_0$ which takes into
account the demagnetizing effects was established from a.c. susceptibility data
at low amplitudes. Losses vs frequency dependencies have been found to agree
nicely with the theoretical model developed for round multifilamentary wires.
Applying this model, the effective resistivity of the matrix was determined for
each tape, by using only measured quantities. For the tape with pure silver
matrix its value was found to be larger than what predicted by the theory for
given metal resistivity and filamentary architecture. On the contrary, in the
sample with a Ag/Mg alloy matrix, an effective resistivity much lower than
expected was determined. We explain these discrepancies by taking into account
the properties of the electrical contact of the interface between the
superconducting filaments and the normal matrix. In the case of soft matrix of
pure Ag, this is of poor quality, while the properties of alloy matrix seem to
provoke an extensive creation of intergrowths which can be actually observed in
this kind of samples. | 0310158v1 |
2007-05-11 | Electrical transport and optical studies of ferromagnetic Cobalt doped ZnO nanoparticles exhibiting a metal-insulator transition | The observed correlation of oxygen vacancies and room temperature
ferromagnetic ordering in Co doped ZnO1-o nanoparticles reported earlier (Naeem
et al Nanotechnology 17, 2675-2680) has been further explored by transport and
optical measurements. In these particles room temperature ferromagnetic
ordering had been observed to occur only after annealing in forming gas. In the
current work the optical properties have been studied by diffuse reflection
spectroscopy in the UV-Vis region and the band gap of the Co doped compositions
has been found to decrease with Co addition. Reflections minima are observed at
the energies characteristic of Co+2 d-d (tethrahedral symmetry) crystal field
transitions, further establishing the presence of Co in substitutional sites.
Electrical transport measurements on palletized samples of the nanoparticles
show that the effect of a forming gas is to strongly decrease the resistivity
with increasing Co concentration. For the air annealed and non-ferromagnetic
samples the variation in the resistivity as a function of Co content are
opposite to those observed in the particles prepared in forming gas. The
ferromagnetic samples exhibit an apparent change from insulator to metal with
increasing temperatures for T>380K and this change becomes more pronounced with
increasing Co content. The magnetic and resistive behaviors are correlated by
considering the model by Calderon et al [M. J. Calderon and S. D. Sarma, Annals
of Physics 2007 (Accepted doi: 10.1016/j.aop.2007.01.010] where the
ferromagnetism changes from being mediated by polarons in the low temperature
insulating region to being mediated by the carriers released from the weakly
bound states in the higher temperature metallic region. | 0705.1593v3 |
2008-01-08 | Impact of silver addition on room temperature magneto-resistance in La0.7Ba0.3MnO3 (LBMO): Agx (x = 0.0, 0.1, 0.2, 0.3, 0.4) | La0.7Ba0.3MnO3 (LBMO):Agx (x = 0.0, 0.1, 0.2, 0.3, and 0.4) composites are
synthesized by solid-state reaction route, the final sintering temperatures are
varied from 1300 (LBMO1300Ag) to 1400 0C (LBMO1400Ag), and their physical
properties are compared as a function of temperature and Ag content. All
samples are crystallized in single phase accompanied by some distortion in main
structural phase peaks at higher angles with increase in silver content. Though
the lattice parameters (a, c) decrease, the b increases slightly with an
increase in Ag content. The scanning electron micrographs (SEM) showed better
grains morphology in terms of size and diffusion of grain boundaries with an
increase in Ag content. In both LBMO1300Ag and LBMO1400Ag series the metal
insulator transition (TMI) and accompanied paramagnetic-ferromagnetic
transition (TC) temperatures are decreased with increase in Ag content. The
sharpness of MI transition, defined by temperature coefficient of resistance
(TCR), is improved for Ag added samples. At a particular content of Ag(0.3),
the TMI and TC are tuned to 300K and maximum magneto-resistance at 7Tesla
applied field (MR7T) of up to 55% is achieved at this temperature, which is
more than double to that as observed for pure samples of the both 1300 and 1400
0C series at same temperature. The MR7T is further increased to above 60% for
LBMOAg(0.4) samples, but is at 270K. The MR7T is measured at varying
temperatures of 5, 100, 200, 300, and 400K in varying fields from +/- 7 Tesla,
which exhibits U and V type shapes. Summarily, the addition of Ag in LBMO
improves significantly the morphology of the grains and results in better
physical properties of the parent manganite system. | 0801.1162v1 |
2011-05-31 | Evidence of electronic phase arrest and glassy ferromagnetic behaviour in (Nd0.4Gd0.3)Sr0.3MnO3 manganite : Comparative study between bulk and nanometric samples | The effect of doping of rare earth Gd 3+ ion replacing Nd 3+ in
Nd0.7Sr0.3MnO3 is investigated in details. Measurements of resistivity,
magnetoresistance, magnetization, linear and non linear ac magnetic
susceptibility on chemically synthesized (Nd0.7-xGdx)Sr0.3MnO3 shows various
interesting features with doping level x=0.3. Comparative study has been
carried out between a bulk and a nanometric sample (grain size ~ 60 nm)
synthesized from the same as prepared powder to maintain identical
stoichiometry. Resistivity of the samples shows strong dependence on the
magnetic field - temperature history. The magnetoresistance of the samples also
show strong irreversibility with respect to sweeping of the field between
highest positive and negative values. Moreover, resistivity is found to
increase with time after field cooling and then switching off the field. All
these phenomena have been attributed to phase separation effect and arrest of
phases in the samples. Furthermore, the bulk sample displays a spin glass like
behaviour as evident from frequency dependence of linear ac magnetic
susceptibility and critical divergence of the nonlinear ac magnetic
susceptibility. The experimentally obtained characteristic time t after
dynamical scaling analysis of the frequency dependence of the ac susceptibility
is found to be t=10-17 s which implies that the system is different from a
canonical spin glass. An unusual frequency dependence of the second harmonic of
ac susceptibility around the magnetic transition temperature led us to
designate the magnetic state of the sample to be glassy ferromagnetic. On
reduction of grain size low field magnetoresistance and phase arrest phenomena
are found to enhance but the glassy state is observed to be destabilized in the
nanometric sample. | 1105.6284v2 |
2013-06-11 | Generation of concentration density maxima of small dispersive coal dust particles in horizontal iodine air filter at air-dust aerosol blow | The spatial distributions of the small dispersive coal dust particles with
the nano and micro sizes in the granular filtering medium with the cylindrical
coal granules in the absorber in the horizontal iodine air filter during its
long term operation at the nuclear power plant are researched. It is shown that
the concentration density maxima of the small dispersive coal dust particles
appear in the granular filtering medium with the cylindrical coal absorbent
granules in the horizontal iodine air filter at an action by the air dust
aerosol blow. The comparison of the measured aerodynamic resistances of the
horizontal and vertical iodine air filters is conducted. The main conclusion is
that the magnitude of the aerodynamic resistance of the horizontal iodine air
filters is much smaller in comparison with the magnitude of the aerodynamic
resistance of the vertical iodine air filters at the same loads of the air dust
aerosol volumes. It is explained that the direction of the air dust aerosol
blow and the direction of the gravitation force in the horizontal iodine air
filter are orthogonal, hence the effective accumulation of the small dispersive
coal dust particles takes place at the bottom of absorber in the horizontal
iodine air filter. It is found that the air dust aerosol stream flow in the
horizontal iodine air filter is not limited by the appearing structures, made
of the precipitated small dispersive coal dust particles, in distinction from
the vertical iodine air filter, in the process of long term operation of the
iodine air filters at the nuclear power plant. | 1306.2853v1 |
2019-09-19 | Improving wafer-scale Josephson junction resistance variation in superconducting quantum coherent circuits | Quantum bits, or qubits, are an example of coherent circuits envisioned for
next-generation computers and detectors. A robust superconducting qubit with a
coherent lifetime of $O$(100 $\mu$s) is the transmon: a Josephson junction
functioning as a non-linear inductor shunted with a capacitor to form an
anharmonic oscillator. In a complex device with many such transmons, precise
control over each qubit frequency is often required, and thus variations of the
junction area and tunnel barrier thickness must be sufficiently minimized to
achieve optimal performance while avoiding spectral overlap between neighboring
circuits. Simply transplanting our recipe optimized for single, stand-alone
devices to wafer-scale (producing 64, 1x1 cm dies from a 150 mm wafer)
initially resulted in global drifts in room-temperature tunneling resistance of
$\pm$ 30%. Inferring a critical current $I_{\rm c}$ variation from this
resistance distribution, we present an optimized process developed from a
systematic 38 wafer study that results in $<$ 3.5% relative standard deviation
(RSD) in critical current ($\equiv \sigma_{I_{\rm c}}/\left\langle I_{\rm c}
\right\rangle$) for 3000 Josephson junctions (both single-junctions and
asymmetric SQUIDs) across an area of 49 cm$^2$. Looking within a 1x1 cm moving
window across the substrate gives an estimate of the variation characteristic
of a given qubit chip. Our best process, utilizing ultrasonically assisted
development, uniform ashing, and dynamic oxidation has shown $\sigma_{I_{\rm
c}}/\left\langle I_{\rm c} \right\rangle$ = 1.8% within 1x1 cm, on average,
with a few 1x1 cm areas having $\sigma_{I_{\rm c}}/\left\langle I_{\rm c}
\right\rangle$ $<$ 1.0% (equivalent to $\sigma_{f}/\left\langle f
\right\rangle$ $<$ 0.5%). Such stability would drastically improve the yield of
multi-junction chips with strict critical current requirements. | 1909.09165v2 |
2014-08-11 | Synchronization of pairwise-coupled, identical, relaxation oscillators based on metal-insulator phase transition devices: A Model Study | Computing with networks of synchronous oscillators has attracted wide-spread
attention as novel materials and device topologies have enabled realization of
compact, scalable and low-power coupled oscillatory systems. Of particular
interest are compact and low-power relaxation oscillators that have been
recently demonstrated using MIT (metal- insulator-transition) devices using
properties of correlated oxides. This paper presents an analysis of the
dynamics and synchronization of a system of two such identical coupled
relaxation oscillators implemented with MIT devices. We focus on two
implementations of the oscillator: (a) a D-D configuration where complementary
MIT devices (D) are connected in series to provide oscillations and (b) a D-R
configuration where it is composed of a resistor (R) in series with a
voltage-triggered state changing MIT device (D). The MIT device acts like a
hysteresis resistor with different resistances in the two different states. The
synchronization dynamics of such a system has been analyzed with purely charge
based coupling using a resistive (Rc) and a capacitive (Cc) element in
parallel. It is shown that in a D-D configuration symmetric, identical and
capacitively coupled relaxation oscillator system synchronizes to an anti-phase
locking state, whereas when coupled resistively the system locks in phase.
Further, we demonstrate that for certain range of values of Rc and Cc, a
bistable system is possible which can have potential applications in
associative computing. In D-R configuration, we demonstrate the existence of
rich dynamics including non-monotonic flows and complex phase relationship
governed by the ratios of the coupling impedance. Finally, the developed
theoretical formulations have been shown to explain experimentally measured
waveforms of such pairwise coupled relaxation oscillators. | 1408.2582v1 |
2014-08-13 | Ferromagnetism, insulator-metal transition and magnetotransport in Pr0.58Ca0.42MnO3 films: role of microstructural perturbations | Magnetic and magnetotransport properties of oriented polycrystalline
Pr0.58Ca0.42MnO3 thin films prepared in flowing oxygen and air ambient has been
investigated. The magnetic ground state of both the films is a frozen cluster
glass. In the air annealed film charge order (CO) is quenched and ferromagnetic
(FM) transition, which appears at TC=148 K is followed by antiferromagnetic
(AFM) transition at TN=104 K. This film shows self-field hysteretic
insulator-metal transition (IMT) at TIMC=89 K and TIMW=148 K in the cooling and
warming cycle, respectively. Application of magnetic field (H) gradually
enhances TIMC and TIMW, reduces the thermoresistive hysteresis and TIM
diminishes. In contrast, the film annealed in flowing oxygen shows a CO
transition, which is followed by FM and AFM transitions. This film shows
appreciably smaller magnetic moment and does not show IMT upto H=20 kOe. As H
is increased to H=30 kOe, IMT having strong thermoresistive hysteresis and
sharp resistivity jumps appears in the cooling and warming cycles. As H
increases to higher values the thermoresistive hysteresis is reduced,
resistivity jumps are observed to disappear and TIM decreases. In the lower
temperature regime the resistivity first decreases slowly with H and then shows
sharp drop. The virgin cycle is not recoverable in subsequent cycles. The
decrement far more pronounced in the oxygen annealed film and occurs at much
higher H suggesting that the frozen cluster glass state is more robust in this
film. The microstructural analysis of the two set of films shows CO quenching,
FM transition and self-field IMT in air annealed film is caused by higher
density of microstructural disorder and lattice defects. The difference in
growth ambience of the two films could give rise to such microstructural
perturbations. | 1408.2979v1 |
2019-12-17 | Metal-to-insulator transition in Pt-doped TiSe$_2$ driven by emergent network of narrow transport channels | Metal-to-insulator transitions (MIT) can be driven by a number of different
mechanisms, each resulting in a different type of insulator -- Change in
chemical potential can induce a transition from a metal to a band insulator;
strong correlations can drive a metal into a Mott insulator with an energy gap;
an Anderson transition, on the other hand, due to disorder leads to a localized
insulator without a gap in the spectrum. Here we report the discovery of an
alternative route for MIT driven by the creation of a network of narrow
channels. Transport data on Pt substituted for Ti in TiSe$_2$ shows a dramatic
increase of resistivity by five orders of magnitude for few % of Pt
substitution, with a power-law dependence of the temperature-dependent
resistivity $\rho(T)$. Our scanning tunneling microscopy data show that Pt
induces an irregular network of nanometer-thick domain walls (DWs) of charge
density wave (CDW) order, which pull charge carriers out of the bulk and into
the DWs. While the CDW domains are gapped, the charges confined to the narrow
DWs interact strongly, with pseudogap-like suppression in the local density of
states, even when they were weakly interacting in the bulk, and scatter at the
DW network interconnects thereby generating the highly resistive state.
Angle-resolved photoemission spectroscopy spectra exhibit pseudogap behavior
corroborating the spatial coexistence of gapped domains and narrow domain walls
with excess charge carriers. | 1912.08246v2 |
2020-06-23 | Electron doping of the layered nickelate La$_4$Ni$_3$O$_{10}$ by aluminum substitution: A combined experimental and DFT study | The physical properties of La$_4$Ni$_3$O$_{10}$ with a 2D-like
Ruddlesden-Popper-type crystal structure are extraordinarily dependent on
temperature and chemical substitution. By introducing Al$^{3+}$ atoms ($x$)
randomly at the Ni-sites, the average oxidation state for the two
non-equivalent Ni-cations is tuned and adopt values below the average of +2.67
in La$_4$Ni$_3$O$_{10}$. La$_4$Ni$_{3-x}$Al$_x$O$_{10}$ is a solid solution for
$x=0.00$ to 1.00, and are prepared by the citric acid method. The samples adopt
a slightly distorted monoclinic structure (P21/a), evidenced by peak broadening
of the (117) reflection. We report on a remarkable effect on the electronic
properties induced by tiny amounts of homogeneously distributed Al-cations,
with clear correspondence between resistivity, magnetization, diffraction, and
DFT data. DFT shows that electronically there is no significant difference
between the non-equivalent Ni atoms and no tendency towards any
Ni$^{3+}$/Ni$^{2+}$ charge ordering. The electron doping via Al-substitution
has a profound effect on electric and magnetic properties. The resistivity
changes from metallic to semiconducting with increasing band-gap at higher
Al-levels, consistent with results from DFT. The metal-to-metal transition
reported for La$_4$Ni$_3$O$_{10}$, which is often interpreted as a charge
density wave, is maintained until $x = 0.15$ Al-level. However, the temperature
characteristics of the resistivity change already at very low Al-levels (below
0.03). A coupling of the metal-to-metal transition to the lattice is evidenced
by an anomaly in the unit cell dimensions. No long-range magnetic order is
detected by powder neutron diffraction. The introduction of the non-magnetic
Al$^{3+}$ changes the Ni$^{3+}$/Ni$^{2+}$ ratio and is likely to block
double-exchange pathways by means of -Ni-O-Al-O-Ni- fragments into the network
of corner shared octahedra with the emergence of possible short-range order in
ferromagnetic like islands. | 2006.12854v1 |
2021-06-03 | A data mining approach for improved interpretation of ERT inverted sections using the DBSCAN clustering algorithm | SUMMARY Geophysical imaging using the inversion procedure is a powerful tool
for the exploration of the Earth's subsurface. However, the interpretation of
inverted images can sometimes be difficult, due to the inherent limitations of
existing inversion algorithms, which produce smoothed sections. In order to
improve and automate the processing and interpretation of inverted geophysical
models, we propose an approach inspired from data mining. We selected an
algorithm known as DBSCAN (Density-Based Spatial Clustering of Applications
with Noise) to perform clustering of inverted geophysical sections. The
methodology relies on the automatic sorting and clustering of data. DBSCAN
detects clusters in the inverted electrical resistivity values, with no prior
knowledge of the number of clusters. This algorithm has the advantage of being
defined by only two parameters: the neighbourhood of a point in the data space,
and the minimum number of data points in this neighbourhood. We propose an
objective procedure for the determination of these two parameters. The proof of
concept described here is applied to simulated ERT (electrical resistivity
tomography) sections, for the following three cases: two layers with a step,
two layers with a rebound, and two layers with an anomaly embedded in the upper
layer. To validate this approach, sensitivity studies were carried out on both
of the above parameters, as well as to assess the influence of noise on the
algorithm's performance. Finally, this methodology was tested on real field
data. DBSCAN detects clusters in the inverted electrical resistivity models,
and the former are then associated with various types of earth materials, thus
allowing the structure of the prospected area to be determined. The proposed
data-mining algorithm is shown to be effective, and to improve the
interpretation of the inverted ERT sections. This new approach has considerable
potential, as it can be applied to any geophysical data represented in the form
of sections or maps. | 2106.01673v1 |
2022-03-13 | Colossal transverse magnetoresistance due to nematic superconducting phase fluctuations in a copper oxide | Electronic anisotropy (or `nematicity') has been detected in all main
families of cuprate superconductors by a range of experimental techniques --
electronic Raman scattering, THz dichroism, thermal conductivity, torque
magnetometry, second-harmonic generation -- and was directly visualized by
scanning tunneling microscope (STM) spectroscopy. Using angle-resolved
transverse resistance (ARTR) measurements, a very sensitive and background-free
technique that can detect 0.5$\%$ anisotropy in transport, we have observed it
also in La$_{2-x}$Sr$_{x}$CuO$_{4}$ (LSCO) for $0.02 \leq x \leq 0.25$.
Arguably the key enigma in LSCO is the rotation of the nematic director with
temperature; this has not been seen before in any material. Here, we address
this puzzle by measuring the angle-resolved transverse magnetoresistance
(ARTMR) in LSCO. We report a discovery of colossal transverse magnetoresistance
(CTMR) -- an order-of-magnitude drop in the transverse resistivity in the
magnetic field of $6\,$T, while none is seen in the longitudinal resistivity.
We show that the apparent rotation of the nematic director is caused by
superconducting phase fluctuations, which are much more anisotropic than the
normal-electron fluid, and their respective directors are not parallel. This
qualitative conclusion is robust and follows straight from the raw experimental
data. We quantify this by modelling the measured (magneto-)conductivity by a
sum of two conducting channels that correspond to distinct anisotropic Drude
and Cooper-pair effective mass tensors. Strikingly, the anisotropy of
Cooper-pair stiffness is significantly larger than that of the normal
electrons, and it grows dramatically on the underdoped side, where the
fluctuations become effectively quasi-one dimensional. | 2203.06769v1 |
2022-04-06 | Planckian properties of 2D semiconductor systems | We describe and discuss the low-temperature resistivity (and the
temperature-dependent inelastic scattering rate) of several different doped 2D
semiconductor systems from the perspective of the Planckian hypothesis
asserting that $\hbar/\tau =k_\mathrm{B}T$ provides a scattering bound, where
$\tau$ is the appropriate relaxation time. The regime of transport considered
here is well-below the Bloch-Gruneisen regime so that phonon scattering is
negligible. The temperature-dependent part of the resistivity is almost
linear-in-$T$ down to arbitrarily low temperatures, with the linearity arising
from an interplay between screening and disorder, connected with carrier
scattering from impurity-induced Friedel oscillations. The temperature
dependence disappears if the Coulomb interaction between electrons is
suppressed. The temperature coefficient of the resistivity is enhanced at lower
densities, enabling a detailed study of the Planckian behavior both as a
function of the materials system and carrier density. Although the precise
Planckian bound never holds, we find somewhat surprisingly that the bound seems
to apply approximately with the scattering rate never exceeding $k_\mathrm{B}
T$ by more than an order of magnitude either in the experiment or in the
theory. In addition, we calculate the temperature-dependent electron-electron
inelastic scattering rate by obtaining the temperature-dependent self-energy
arising from Coulomb interaction, also finding it to obey the Planckian bound
within an order of magnitude at all densities and temperatures. We introduce
the concept of a generalized Planckian bound where $\hbar/\tau$ is bounded by
$\alpha k_\mathrm{B} T$ with $\alpha\sim 10$ or so in the super-Planckian
regime with the strict Planckian bound of $\alpha$=1 being a nongeneric
finetuned situation. | 2204.02982v3 |
2022-06-18 | Radiation resistance in simulated metallic core-shell nanoparticles | We present molecular dynamics (MD) simulations of radiation damage in pure Fe
nanoparticles (NP) and bimetallic FeCu core-shell nanoparticles (CSNP). The
CSNP includes a perfect body centered cubic (bcc) Fe core coated with a
face-centered cubic (fcc) Cu shell. Irradiation with Fe Primary Knock-on Atoms
(PKA) with energies between 1 and 7 keV leads to point defects, without
clustering beyond divacancies and very few slightly larger vacancy clusters,
and without interstitial clusters, unlike what happens in bulk at the same PKA
energies. The Fe-Cu interface and shell can act as a defect sink, absorbing
radiation-induced damage and, therefore, the final number of defects in the Fe
core is significantly lower than in the Fe NP. In addition, the Cu shell
substantially diminishes the number of sputtered Fe atoms, acting as a barrier
for recoil ejection. Structurally, the Cu shell responds to the stress
generated by the collision cascade by creating and destroying stacking faults
across the shell width, which could also accommodate further irradiation
defects. Sputtering yield (Y) is underestimated by BCA, which is also expected
since the simulation is for a thin film at normal incidence. We also compare MD
defect production to bulk predictions of the analytic Athermal Recombination
Corrected Displacements Per Atom (arc-dpa) model. The number of vacancies in
the Fe core is only slightly lower than arc-dpa predictions, but the number of
interstitials is reduced by about one order of magnitude compared to vacancies,
at 5 keV. According to the radiation resistance found for FeCu CSNP in our
simulations, this class of nanomaterial could be suitable for developing new
radiation resistant coatings, nanostructured components, and shields for use in
extreme environments, for instance, in nuclear energy and astrophysical
applications. | 2206.09063v2 |
2022-10-31 | Modeling disks and magnetic outflows around a forming massive star: I. Investigating the two layer-structure of the accretion disk | Like their lower mass siblings, massive protostars can be expected to: a) be
surrounded by circumstellar disks and b) launch magnetically-driven jets and
outflows. The disk formation and global evolution is thereby controlled by
advection of angular momentum from large scales, the efficiency of magnetic
braking and the resistivity of the medium, and the internal thermal and
magnetic pressures of the disk. We perform a series of 30 simulations of a
massive star forming from the gravitational collapse of a molecular cloud
threaded by an initially-uniform magnetic field, starting from different values
for the mass of the cloud, its initial density and rotation profiles, its
rotational energy content, the magnetic field strength, and the resistivity of
the material. The gas and dust is modeled with the methods of resistive
magnetohydrodynamics, also considering radiation transport of thermal emission
and self-gravity. After the initial infall phase dominated by the gravitational
collapse, an accretion disk is formed, shortly followed by the launching of
magnetically-driven outflows. Two layers can be distinguished in the accretion
disk: a thin layer, vertically supported by thermal pressure, and a thick
layer, vertically supported by magnetic pressure. We observe the effects of
magnetic braking in the inner ~50 au of the disk at late times in our fiducial
case. The parameter study reveals that the size of the disk is mostly
determined by the density and rotation profiles of the initial mass reservoir
and not by the magnetic field strength. Magnetic pressure can slightly increase
the size of the accretion disk, while magnetic braking is more relevant in the
innermost parts of the disk as opposed to the outer disk. From the parameter
study, we infer that multiple initial conditions for the onset of gravitational
collapse are able to produce a given disk size and protostellar mass. | 2210.17220v1 |
2023-01-05 | Self-Assembly of Soot Nanoparticles on the Surface of Resistively Heated Carbon Microtubes in Near-Hexagonal Arrays of Micropyramids | Almost regular hexagonal arrays of a few micrometers tall and wide
micropyramids consisting of soot nano-particles are formed on the surface of
graphitized hollow filaments, which are resistively heated to
~1800$^\circ$C-2400$^\circ$C in an Ar atmosphere containing trace amounts of
oxygen (~300 p.p.m.). At the higher temperatures (T>2300$^\circ$C,
approximately) the soot particles are represented mainly by multi-shell carbon
nano-onions. The height and the width of the pyramids is strongly dependent on
the temperature of the resistive heating, diminishing from 5-10mkm at
T=1800$^\circ$C to 1mkm at 2300-2400$^\circ$C. Quasi-hexagonal arrays of the
micropyramids are organized in the convex ``craters'' on the surface of the
microtubes, which grow with the time of the thermal treatment. The pyramids are
pointing always normally to the surface of the craters, except at the
boundaries between the craters, where the normal direction is not well defined.
The pyramids are soft and can be easy destroyed by touching them, but can be
hardened by heating them in the oxygen-free atmosphere. The pyramids are
observed only on the exterior surface of the microtubes, but not on their inner
surface. This suggests that the thermophoretic force generated by a strong
temperature gradient near the external surface of the tubes may be the cause of
the micropyramids formation. Electrostatic charging of the soot nanoparticles
due to thermionic emission may also be relevant to this phenomenon. The
micropyramids can function as field emission point sources, as demonstrated
with the use of a micro-nanoprobing station, mounted in a scanning electron
microscope. | 2301.05023v1 |
2023-03-19 | Disentangling superconductor and dielectric microwave losses in sub-micron $\rm Nb$/$\rm TEOS-SiO_2$ interconnects using a multi-mode microstrip resonator | Understanding the origins of power loss in superconducting interconnects is
essential for the energy efficiency and scalability of superconducting digital
logic. At microwave frequencies, power dissipates in both the dielectrics and
superconducting wires, and these losses can be of comparable magnitude. A novel
method to accurately disentangle such losses by exploiting their frequency
dependence using a multi-mode transmission line resonator, supported by a
geometric factor concept and a 3D superconductor finite element method (FEM)
modeling, is described. Using the method we optimized a planarized fabrication
process of reciprocal quantum logic (RQL) for the interconnect loss at 4.2 K
and GHz frequencies. The interconnects are composed of niobium ($\rm Nb$)
insulated by silicon dioxide made with a tetraethyl orthosilicate precursor
($\rm TEOS-SiO_2$). Two process generations use damascene fabrication, and the
third one uses Cloisonn\'{e} fabrication. For all three, $\rm TEOS-SiO_2$
exhibits a dielectric loss tangent $\tan \delta = 0.0012 \pm 0.0001$,
independent of $\rm Nb$ wire width over $0.25 - 4 \: \mu m$. The $\rm Nb$ loss
varies with both the processing and the wire width. For damascene fabrication,
scanning transmission electron microscopy (STEM) and energy dispersive X-ray
spectroscopy (EDS) reveal that Nb oxide and Nb grain growth orientation
increase the loss above the Bardeen Cooper Schrieffer (BCS) minimum theoretical
resistance $R _{BCS}$. For Cloisonn\'{e} fabrication, the $0.25 \: \mu m$ wide
$\rm Nb$ wires exhibit an intrinsic resistance $R_s = 13 \pm 1.4 \: \mu \Omega$
at 10 GHz, which is below $R_{BCS} \approx 17 \: \mu \Omega$. That is arguably
the lowest resistive loss reported for $\rm Nb$. | 2303.10685v1 |
2023-07-31 | Semiconducting transport in Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O sintered from Pb$_2$SO$_5$ and Cu$_3$P | The very recent claim on the discovery of ambient-pressure room-temperature
superconductivity in modified lead-apatite has immediately excited sensational
attention in the entire society, which is fabricated by sintering lanarkite
(Pb2SO5) and copper(I) phosphide (Cu$_3$P). To verify this exciting claim, we
have successfully synthesized Pb$_2$SO$_5$, Cu$_3$P, and finally the modified
lead-apatite Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O. Detailed electrical transport and
magnetic properties of these compounds were systematically analyzed. It turns
out that Pb$_2$SO$_5$ is a highly insulating diamagnet with a room-temperature
resistivity of ~7.18x10$^9$ Ohm.cm and Cu$_3$P is a paramagnetic metal with a
room-temperature resistivity of ~5.22x10$^{-4}$ Ohm.cm. In contrast to the
claimed superconductivity, the resulting Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O
compound sintered from Pb$_2$SO$_5$ and Cu$_3$P exhibits semiconductor-like
transport behavior with a large room-temperature resistivity of ~1.94x10$^4$
Ohm.cm although our compound shows greatly consistent x-ray diffraction
spectrum with the previously reported structure data. In addition, when a
pressed Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O pellet is located on top of a commercial
Nd$_2$Fe$_{14}$B magnet at room temperature, no repulsion could be felt and no
magnetic levitation was observed either. These results imply that the claim of
a room-temperature superconductor in modified lead-apatite may need more
careful re-examination, especially for the electrical transport properties. | 2307.16802v1 |
2023-08-11 | Observation of integer and fractional quantum anomalous Hall effects in twisted bilayer MoTe2 | The interplay between strong correlations and topology can lead to the
emergence of intriguing quantum states of matter. One well-known example is the
fractional quantum Hall effect, where exotic electron fluids with fractionally
charged excitations form in partially filled Landau levels. The emergence of
topological moir\'e flat bands provides exciting opportunities to realize the
lattice analogs of both the integer and fractional quantum Hall states without
the need for an external magnetic field. These states are known as the integer
and fractional quantum anomalous Hall (IQAH and FQAH) states. Here, we present
direct transport evidence of the existence of both IQAH and FQAH states in
twisted bilayer MoTe2 (AA stacked). At zero magnetic field, we observe
well-quantized Hall resistance of h/e2 around moir\'e filling factor {\nu} = -1
(corresponding to one hole per moir\'e unit cell), and nearly-quantized Hall
resistance of 3h/2e2 around {\nu} = -2/3, respectively. Concomitantly, the
longitudinal resistance exhibits distinct minima around {\nu} = -1 and -2/3.
The application of an electric field induces topological quantum phase
transition from the IQAH state to a charge transfer insulator at {\nu} = -1,
and from the FQAH state to a generalized Wigner crystal state, further
transitioning to a metallic state at {\nu} = -2/3. Our study paves the way for
the investigation of fractionally charged excitations and anyonic statistics at
zero magnetic field based on semiconductor moir\'e materials. | 2308.06177v3 |
2023-10-15 | Structural and physical properties of the chiral antiferromagnet CeRhC$_2$ | We report a study of the structural, magnetic, transport, and thermodynamic
properties of polycrystalline samples of CeRhC$_2$. CeRhC$_2$ crystallizes in a
tetragonal structure with space group $P4_1$ and it orders
antiferromagnetically below $T_\textrm{N1} \approx$ 1.8 K. Powder neutron
diffraction measurements reveal a chiral magnetic structure with a single
propagation vector $Q_m = (1/2,1/2,0.228(5))$, indicating an antiferromagnetic
arrangement of Ce magnetic moments in the $ab$-plane and incommensurate order
along the $c$-axis with a root-mean-square ordered moment of $m_\textrm{ord}$=
0.68 $\mu_\textrm{B}$/Ce. Applying a magnetic field suppresses the N\'{e}el
temperature $T_\textrm{N1}$ to zero near $\mu_0H_\textrm{c1}\sim$0.75 T. A
second antiferromagnetic phase ($T_\textrm{N2}$), however, becomes apparent in
electrical resistivity, Hall and heat capacity measurements in fields above 0.5
T and extrapolates to zero temperature at $\mu_0H_\textrm{c2}\sim$ 1 T.
Electrical resistivity measurements reveal that LaRhC$_2$ is a semiconductor
with a bandgap of $E_\textrm{g}\sim24$ meV; whereas, resistivity and Hall
measurements indicate that CeRhC$_2$ is a semimetal with a low carrier
concentration of $n\sim10^{20}$ cm$^{-3}$. With applied hydrostatic pressure,
the zero-field antiferromagnetic transition of CeRhC$_2$ is slightly enhanced
and CeRhC$_2$ becomes notably more metallic up to 1.36 GPa. The trend toward
metallicity is in line with density-functional calculations that indicate that
both LaRhC$_2$ and CeRhC$_2$ are semimetals, but the band overlap is larger for
CeRhC$_2$, which has a smaller unit cell volume that its La counterpart. This
suggests that the bandgap closes due to a lattice contraction when replacing La
with Ce in RRhC$_2$ (R = rare-earth), in agreement with experimental results. | 2310.09904v1 |
2023-12-16 | Multiple magnetic transitions, metamagnetism and large magnetoresistance in GdAuGe single crystals | We report the physical properties of GdAuGe single crystals, which were grown
using Bi flux. The powder x-ray diffraction data shows that the compound
crystallizes in hexagonal NdPtSb-type structure (space group P63mc).
Magnetization measurements performed for field configuration H||c and H||ab
show that GdAuGe orders antiferromagnetically at the Neel temperature, TN =
17.2 K. Around this temperature, heat capacity and electrical resistivity data
exhibit prominent anomaly due to the antiferromagnetic (AFM) transition. In
addition to an AFM phase transition, the magnetization data for H||c display
the signature of field-induced metamagnetic (MM) transitions below TN. The
critical field range for these transitions vary from 0.2 to 6.2 T. The critical
fields for the MM transitions decrease with increasing temperature and approach
zero value for temperature approaching TN. Interestingly, the magnetoresistance
(MR) data (for H||c) record a sharp increase in values at the critical fields
that coincide with those seen in magnetization data, tracking the presence of
MM transitions. MR is positive and large (169% at 9 T and 2 K) at low
temperatures. Above TN, MR becomes small and switches to negative values. Hall
resistivity data reveal the predominance of hole charge carriers in the system.
In addition, we observe an emergence of step-like feature in the Hall
resistivity data within the field range of second MM, and a significantly large
anomalous Hall conductivity of 1270 {\Omega}-1 cm-1 at 2 K. The H-T phase
diagram constructed from our detailed magnetization and magnetotransport
measurements reveals multiple intricate magnetic phase transitions. The
electronic and magnetic structure of GdAuGe are also thoroughly investigated
using first-principles methods. The electronic band structure calculations
reveal that GdAuGe is a Dirac nodal-line semimetal. | 2312.10352v1 |
2024-01-31 | Effect of annealing on the corrosion-fatigue strength and hot salt corrosion resistance of fine-grained titanium near-α alloy Ti-5Al-2V obtained by Rotary Swaging | The corrosion-fatigue strength in 3% aqueous NaCl solution and the resistance
against hot salt corrosion (HSC) of the fine-grained near-a alloy Ti-5Al-2V
(Russian analog of Grade 9 titanium alloy with increased aluminum content) has
been studied. The properties of the Ti-5Al-2V alloy in the coarse-grained
state, in the fine-grained after cold Rotary Swaging (RS), in partly
recrystallized state, and in fully recrystallized one have been investigated.
The mechanical properties of the alloy were characterized using compression
tests and microhardness measurements. The effects of RS and of the annealing
temperature and time on the character of corrosion destruction of the surface
and on the composition of the products of the HSC were studied. RS was shown to
result in an increase in the depth of the intergranular corrosion defects while
the recrystallization annealing promotes the increasing of the corrosion
resistance of the Ti-5Al-2V titanium alloy. The parameters of the Basquin
equation for the corrosion-fatigue curves for the near-a Ti-5Al-2V alloy in the
coarse-grained state, in the severely strained one, and after recrystallization
annealing were determined for the first time. An effect of nonmonotonous
dependencies of the slopes of the corrosion-fatigue curves for the strained
near-a Ti-5Al-2V alloy on the recrystallization annealing temperature has been
observed. | 2401.17659v1 |
2024-02-18 | Combined X-ray diffraction, electrical resistivity, and $ab$ $initio$ study of (TMTTF)$_2$PF$_6$ under pressure: implications to the unified phase diagram | We present a combined experimental and theoretical study on the
quasi-one-dimensional organic conductor (TMTTF)$_2$PF$_6$, and elucidate the
variation of its physical properties under pressure. We fully resolve the
crystal structure by single crystal x-ray diffraction measurements using a
diamond anvil cell up to 8 GPa, and based on the structural data, we perform
first-principles density-functional theory calculations and derive the $ab$
$initio$ extended Hubbard-type Hamiltonians. Furthermore, we compare the
behavior of the resistivity measured up to 3 GPa using a BeCu clamp-type cell
and the ground state properties of the obtained model numerically calculated by
the many-variable variational Monte Carlo method. Our main findings are as
follows: i) The crystal was rapidly compressed up to about 3 GPa where the
volume drops to 80% and gradually varies down to 70% at 8 GPa. The transfer
integrals increase following such behavior whereas the screened Coulomb
interactions decrease, resulting in a drastic reduction of correlation effect.
ii) The degree of dimerization in the intrachain transfer integrals, as the
result of the decrease in structural dimerization together with the change in
the intermolecular configuration, almost disappears above 4 GPa; the interchain
transfer integrals also show characteristic variations under pressure. iii) The
results of identifying the characteristic temperatures in the resistivity and
the charge and spin orderings in the calculations show an overall agreement:
The charge ordering sensitively becomes unstable above 1 GPa, while the spin
ordering survives up to higher pressures. These results shed light on the
similarities and differences between applying external pressure and
substituting the chemical species (chemical pressure). | 2403.13816v1 |
2024-03-29 | Heat Transfer Coefficients of Moving Particle Beds from Flow-Dependent Particle Bed Thermal Conductivity and Near-Wall Resistance | Determination of heat transfer coefficients for flowing packed particle beds
is essential to the design of particle heat exchangers, and other thermal
processes. While such dense granular flows fall into the well-known plug-flow
regime, the discrete nature of granular materials alters the thermal transport
processes in both the near-wall and bulk regions of flowing particle beds from
their stationary counterparts. As a result, heat transfer correlations based on
the stationary particle bed thermal conductivity could be inadequate for
flowing particles in a heat exchanger. Earlier works have achieved reasonable
agreement with experiments by treating granular media as a plug-flow continuum
with a near-wall thermal resistance in series. However, the properties of the
continuum were often obtained from measurements on stationary beds owing to the
difficulty of flowing bed measurements. In this work, it was found that the
properties of a stationary bed are highly sensitive to the method of particle
packing and there is a decrease in the particle bed thermal conductivity and
increase in the near-wall thermal resistance, measured as an effective air gap
thickness, on the onset of particle flow. These variations in the
thermophysical properties of stationary and flowing particle beds can lead to
errors in heat transfer coefficient calculations. Therefore, the heat transfer
coefficients for granular flows were calculated using experimentally determined
flowing particle bed thermal conductivity and near-wall air gap for ceramic
particles -CARBOCP40/100(275 um), HSP40/70(404um) and HSP16/30(956um); at
velocities of 5-15mms-1; and temperatures of 300-650C. The thermal conductivity
and air gap values for CP40/100 and HSP40/70 were further used to calculate
heat transfer coefficients across different particle bed temperatures and
velocities for different parallel-plate heat exchanger dimensions. | 2403.19892v2 |
2024-04-03 | Bacterial cell death: Atomistic simulations reveal pore formation as a mode of action of structurally nano engineered star peptide polymers | Multidrug resistance (MDR) to conventional antibiotics is one of the most
urgent global health threats, necessitating the development of effective and
biocompatible antimicrobial agents that are less inclined to provoke
resistance. Structurally Nanoengineered Antimicrobial Peptide Polymers (SNAPPs)
are a novel and promising class of such alternatives. These star-shaped
polymers are made of a dendritic core with multiple arms made of co-peptides
with varying amino acid sequences. Through a comprehensive set of in vivo
experiments, we (Nature Microbiology, 1, 16162, 2016) showed that SNAPPs with
arms made of random blocks of lysine (K) and valine (V) residues exhibit
sub-micron M efficacy against Gram-negative and Gram-positive bacteria tested.
Cryo-TEM images suggested pore formation by SNAPP with random block co-peptide
arms as one of their mode of actions. However, the molecular mechanisms
responsible for this mode of action of SNAPP were not fully understood. To
address this gap, we employed atomistic molecular dynamics simulation technique
to investigate the influence of three different sequences of amino acids,
namely 1) alternating block KKV 2) random block and 3) di-block motifs on
secondary structure of their arms and SNAPP's overall configuration as well as
their interactions with lipid bilayer. We, for the first time identified a
step-by-step mechanism through which alternating block and random SNAPPs
interact with lipid bilayer and leads to pore formation, hence cell death.
These insights provide a strong foundation for further optimization of the
chemical structure of SNAPPs for maximum performance against MDR bacteria,
therefore offering a promising avenue for addressing antibiotic resistance and
development of effective antibacterial agents. | 2404.02501v3 |
2019-07-30 | Investigating radiation damage in nuclear energy materials using JANNuS multiple ion beams | Ion accelerators have been used by material scientists for decades to
investigate radiation damage formation in nuclear materials and thus to emulate
neutron-induced changes. The versatility of conditions in terms of particle
energy, dose rate, fluence, etc., is a key asset of ion beams allowing for
fully instrumented analytical studies. In addition, very short irradiation
times and handling of non-radioactive samples dramatically curtail the global
cost and duration as compared to in-reactor testing. Coupling of two or more
beams, use of heated/cooled sample holders, and implementation of in situ
characterization and microscopy pave the way to real time observation of
microstructural and property evolution in various extreme radiation conditions
more closely mimicking the nuclear environments. For these reasons, multiple
ion beam facilities have been commissioned worldwide. In France, under the
auspices of the Universit{\'e} Paris-Saclay, the JANNuS platform for 'Joint
Accelerators for Nanosciences and Nuclear Simulation' comprises five ion
implanter and electrostatic accelerators with complementary performances. At
CSNSM (CNRS \& Univ Paris-Sud, Orsay), a 200 kV Transmission Electron
Microscope is coupled to an accelerator and an implanter for in situ
observation of microstructure modifications induced by ion beams in a material,
making important contribution to the understanding of physical phenomena at the
nanoscale. At CEA Paris-Saclay, the unique triple beam facility in Europe
allows the simultaneous irradiation with heavy ions (like Fe, W) for nuclear
recoil damage and implantation of a large array of ions including gasses for
well-controlled modelling-oriented experiments. Several classes of materials
are of interest for the nuclear industry ranging from metals and alloys, to
oxides or glasses and carbides. This paper gives selected examples that
illustrate the use of JANNuS ion beams in investigating the radiation
resistance of structural materials for today's and tomorrow's nuclear reactors. | 1908.00627v1 |
1997-05-20 | Low-temperature resistivity of single crystals YBa_2Cu_3O_{6+x} in the normal state | A scan of the superconductor -- nonsuperconductor transformation in single
crystals YBa_2Cu_3O_{6+x} (x about 0.37) was done in two alternative ways,
namely, by applying the magnetic field and by reducing the hole concentration
through the oxygen rearrangement. The in-plane normal-state resistivity
\rho_{ab} obtained in both cases was quite similar; its temperature dependence
can be fitted by logarithmic law in the temperature range of almost two
decades. However, a different representation of the \sigma_{ab}=1/\rho_{ab} by
a power law typical for a 3D-material near a metal -- insulator transition is
also plausible. The vertical conductivity \sigma_c=1/\rho_c followed the power
law and neither \sigma_c(T), nor \rho_c(T) could be fitted by log(T). It
follows from the \rho_c measurements that the transformation at T=0 is split
into two transitions: superconductor -- normal-metal and normal-metal --
insulator. In our samples, they are distanced in the oxygen content by \Delta
x\approx0.025. | 9705197v2 |
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