publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
|---|---|---|---|
2017-10-30 | Analysis of the measurements of anisotropic a.c. vortex resistivity in tilted magnetic fields | Measurements of the high-frequency complex resistivity in superconductors are
a tool often used to obtain the vortex parameters, such as the vortex
viscosity, the pinning constant and the depinning frequency. In anisotropic
superconductors, the extraction of these quantities from the measurements faces
new difficulties due to the tensor nature of the electromagnetic problem. The
problem is specifically intricate when the magnetic field is tilted with
respect to the crystallographic axes. Partial solutions exist in the
free-flux-flow (no pinning) and Campbell (pinning dominated) regimes. In this
paper we develop a full tensor model for the vortex motion complex resistivity,
including flux-flow, pinning, and creep. We give explicit expressions for the
tensors involved. We obtain that, despite the complexity of the physics, some
parameters remain scalar in nature. We show that under specific circumstances
the directly measured quantities do not reflect the true vortex parameters, and
we give procedures to derive the true vortex parameters from measurements taken
with arbitrary field orientations. Finally, we discuss the applicability of the
angular scaling properties to the measured and transformed vortex parameters
and we exploit these properties as a tool to unveil the existence of
directional pinning. | 1710.11485v1 |
2018-03-06 | Effect of charge ordering on the electrical properties and magnetoresistance of manganites | The Monte Carlo Ferromagnetic Ising model was used to study the electrical
properties of manganese oxides due to the charge ordering phase occurring at
doping, x = 0.5. The half-doped manganites have an insulator antiferromagnetic
ground state. We calculated the internal energy, specific heat, resistivity and
the magneto-resistance, MR, with parallel and anti-parallel applied magnetic
fields. Our simulation reveals that the resistivity decreases exponentially and
the electric current increases with increasing temperature according the free
charge increase, to transport from an insulator to conductor phase. The
magnetoresistance has negative small values with parallel magnetic field but
has positive high values with unti-parallel magnetic field. The obtained
semiconductor-metal transition behavior candidates the half-doped manganites to
be very good semiconductors diode junctions. | 1803.02283v1 |
2018-05-21 | Holographic DC Conductivity for Backreacted Nonlinear Electrodynamics with Momentum Dissipation | We consider a holographic model with the charge current dual to a general
nonlinear electrodynamics (NLED) field. Taking into account the backreaction of
the NLED field on the geometry and introducing axionic scalars to generate
momentum dissipation, we obtain expressions for DC conductivities with a finite
magnetic field. The properties of the in-plane resistance are examined in
several NLED models. For Maxwell-Chern-Simons electrodynamics, negative
magneto-resistance and Mott-like behavior could appear in some parameter space
region. Depending on the sign of the parameters, we expect the NLED models to
mimic some type of weak or strong interactions between electrons. In the latter
case, negative magneto-resistance and Mott-like behavior can be realized at low
temperatures. Moreover, the Mott insulator to metal transition induced by a
magnetic field is also observed at low temperatures. | 1805.07913v2 |
2018-06-23 | Magnetic and magnetoresistive behavior of the ferromagnetic heavy fermion YbNi$_2$ | We present a study on the magnetic susceptibility $\chi(T)$ and electrical
resistance, as a function of temperature and magnetic field $R(T,H)$, of the
ferromagnetic heavy fermion YbNi$_2$. The X-ray diffraction analysis shows that
the synthesized polycrystalline samples crystallizes in the cubic Laves phase
structure C15, with a spatial group $Fd\overline{3}m$. The magnetic
measurements indicate a ferromagnetic behavior with transition temperature at 9
K. The electrical resistance is metallic-like at high temperatures and no
signature of Kondo effect was observed. In the ferromagnetic state, the
electrical resistance can be justified by electron-magnon scattering
considering the existence of an energy gap in the magnonic spectrum. The energy
gap was determined for various applied magnetic fields. Magnetoresistance as a
function of applied magnetic field, subtracted from the $R(T,H)$ curves at
several temperatures, is negative from 2 K until about 40 K for all applied
magnetic fields. The negative magnetoresistance originates from the suppression
of magnetic disorder by the magnetic field. | 1806.08881v1 |
2018-09-17 | Resisting Selfish Mining Attacks in the Bicomp | Selfish mining, which is an attack on the integrity of the Bitcoin network,
was first proposed by Cornell researchers Emin Gun Sirer and Ittay Eyal in
2013. Selfish mining attack also exists in most Nakamoto consensus protocols.
Generally speaking, selfish mining strategy can comprise a Nakamoto consensus
system with less than 25% mining power of the whole system. We have discussed
how the Bicomp can resist selfish mining in our former paper "Bicomp: A Bilayer
Scalable Nakamoto Consensus Protocol". In this technical report, we give a
detailed derivation on the conditions a selfish attacker should meet to earn
more revenues through selfish mining. And we also get a conclusion that through
adjusting macroblock difficulties together with tenure lengths, the Bicomp
protocol has high resistant towards selfish mining. | 1809.06289v1 |
2017-03-30 | Deep Neural Network Optimized to Resistive Memory with Nonlinear Current-Voltage Characteristics | Artificial Neural Network computation relies on intensive vector-matrix
multiplications. Recently, the emerging nonvolatile memory (NVM) crossbar array
showed a feasibility of implementing such operations with high energy
efficiency, thus there are many works on efficiently utilizing emerging NVM
crossbar array as analog vector-matrix multiplier. However, its nonlinear I-V
characteristics restrain critical design parameters, such as the read voltage
and weight range, resulting in substantial accuracy loss. In this paper,
instead of optimizing hardware parameters to a given neural network, we propose
a methodology of reconstructing a neural network itself optimized to resistive
memory crossbar arrays. To verify the validity of the proposed method, we
simulated various neural network with MNIST and CIFAR-10 dataset using two
different specific Resistive Random Access Memory (RRAM) model. Simulation
results show that our proposed neural network produces significantly higher
inference accuracies than conventional neural network when the synapse devices
have nonlinear I-V characteristics. | 1703.10642v1 |
2019-02-01 | Achieving sub-1 Ohm-mm Non-Recess S/D Contact Resistance in GaN HEMTs Utilizing Simple CMOS Compatible La/Ti/Al/Ti Metal Contacts | In this paper, we report the use of lanthanum (La) in S/D contacts of GaN
HEMTs, achieving 0.97 Ohm-mm contact resistance without S/D recess. The HEMTs
show well-behaved electrical characteristics and satisfactory reliability. Our
studies show that La, a CMOS compatible metal, is promising to lower GaN HEMT
S/D contact resistance. La's low work function (3.5 eV) is beneficial for
reducing the barrier between the metals and GaN. The Ohmic contact formation
mechanism involved was shown to be different from conventional Ti/Al films.
Spherical-shaped high-La regions formed near the surface during annealing. La
diffuses into the AlGaN layer, and the overlap of La and Al peaks is
significantly increased compared with that before annealing. | 1902.00227v1 |
2019-02-05 | Resistive dissipative magnetohydrodynamics from the Boltzmann-Vlasov equation | We derive the equations of motion of relativistic, resistive, second-order
dissipative magnetohydrodynamics from the Boltzmann-Vlasov equation using the
method of moments. We thus extend our previous work [Phys. Rev. D 98, 076009
(2018)], where we only considered the non-resistive limit, to the case of
finite electric conductivity. This requires keeping terms proportional to the
electric field $E^\mu$ in the equations of motions and leads to new transport
coefficients due to the coupling of the electric field to dissipative
quantities. We also show that the Navier-Stokes limit of the charge-diffusion
current corresponds to Ohm's law, while the coefficients of electrical
conductivity and charge diffusion are related by a type of Wiedemann-Franz law. | 1902.01699v1 |
2019-07-23 | Magnetotransport properties of granular oxide-segregated CoPtCr films for applications in future magnetic memory technology | Magnetotransport properties of granular oxide-segregated CoPtCr films were
studied on both macroscopic and microscopic length scales by performing bulk
and point-contact magnetoresistance measurements, respectively. Such a
perpendicular magnetic medium is used in state-of-the-art hard disc drives and
if combined with magnetoresistive phenomena (for read/write operations) may
lead to a novel concept for magnetic recording with high areal density. While
the bulk measurements on the films showed only small variations in dc
resistance as a function of applied magnetic field (magnetoresistance of less
than 0.02 %), the point-contact measurements revealed
giant-magnetoresistance-like changes in resistance with up to 50,000 % ratios.
The observed magnetorestive effect could be attributed to a tunnel
magnetoresistance between CoPtCr grains with different coercivity. The
tunneling picture of electronic transport in our granular medium was confirmed
by the observation of tunneling-like current-voltage characteristics and bias
dependence of magnetoresistance; both the point-contact resistance and
magnetoresistance were found to decrease with the applied dc bias. | 1907.09675v1 |
2020-02-01 | Isotropically conducting (hidden) quantum Hall stripe phases in a two-dimensional electron gas | Quantum Hall stripe (QHS) phases, predicted by the Hartree-Fock theory, are
manifested in GaAs-based two-dimensional electron gases as giant resistance
anisotropies. Here, we predict a ``hidden'' QHS phase which exhibits
\emph{isotropic} resistivity whose value, determined by the density of states
of QHS, is independent of the Landau index $N$ and is inversely proportional to
the Drude conductivity at zero magnetic field. At high enough $N$, this phase
yields to an Ando-Unemura-Coleridge-Zawadski-Sachrajda phase in which the
resistivity is proportional to $1/N$ and to the ratio of quantum and transport
lifetimes. Experimental observation of this border should allow one to find the
quantum relaxation time. | 2002.00154v6 |
2007-10-25 | Simulation Methodology for Analysis of Substrate Noise Impact on Analog / RF Circuits Including Interconnect Resistance | This paper reports a novel simulation methodology for analysis and prediction
of substrate noise impact on analog / RF circuits taking into account the role
of the parasitic resistance of the on-chip interconnect in the impact
mechanism. This methodology allows investigation of the role of the separate
devices (also parasitic devices) in the analog / RF circuit in the overall
impact. This way is revealed which devices have to be taken care of (shielding,
topology change) to protect the circuit against substrate noise. The developed
methodology is used to analyze impact of substrate noise on a 3 GHz LC-tank
Voltage Controlled Oscillator (VCO) designed in a high-ohmic 0.18 $\mu$m 1PM6
CMOS technology. For this VCO (in the investigated frequency range from DC to
15 MHz) impact is mainly caused by resistive coupling of noise from the
substrate to the non-ideal on-chip ground interconnect, resulting in analog
ground bounce and frequency modulation. Hence, the presented test-case reveals
the important role of the on-chip interconnect in the phenomenon of substrate
noise impact. | 0710.4723v1 |
2014-01-27 | Transport near the Ising-nematic quantum critical point of metals in two dimensions | We consider two-dimensional metals near a Pomeranchuk instability which
breaks 90$^\circ$ lattice rotation symmetry. Such metals realize
strongly-coupled non-Fermi liquids with critical fluctuations of an
Ising-nematic order. At low temperatures, impurity scattering provides the
dominant source of momentum relaxation, and hence a non-zero electrical
resistivity. We use the memory matrix method to compute the resistivity of this
non-Fermi liquid to second order in the impurity potential, without assuming
the existence of quasiparticles. Impurity scattering in the $d$-wave channel
acts as a random "field" on the Ising-nematic order. We find contributions to
the resistivity with a nearly linear temperature dependence, along with more
singular terms; the most singular is the random-field contribution which
diverges in the limit of zero temperature. | 1401.7012v2 |
2016-03-21 | Spin Hall effects in mesoscopic Pt films with high resistivity | The energy efficiency of the spin Hall effects (SHE) can be enhanced if the
electrical conductivity is decreased without sacrificing the spin Hall
conductivity. The resistivity of Pt films can be increased to 150-300
{\mu}{\Omega}*cm by mesoscopic lateral confinement, thereby decreasing the
conductivity. The SHE and inverse spin Hall effects (ISHE) in these mesoscopic
Pt films are explored at 10 K by using the nonlocal spin injection/detection
method. All relevant physical quantities are determined in-situ on the same
substrate, and a quantitative approach is developed to characterize all
processes effectively. Extensive measurements with various Pt thickness values
reveal an upper limit for the Pt spin diffusion length: {\lambda}_pt<0.8 nm.
The average product of {\lambda}_pt and the Pt spin Hall angle {\alpha}_H is
substantial: {\alpha}_H*{\lambda}_pt=(0.142 +/- 0.040)nm for 4 nm thick Pt,
though a gradual decrease is observed at larger Pt thickness. The results
suggest enhanced spin Hall effects in resistive mesoscopic Pt films. | 1603.06567v3 |
2017-05-07 | Penetration of fast projectiles into resistant media: from macroscopic to subatomic projectiles | The penetration of a fast projectile into a resistant medium is a complex
process that is suitable for simple modeling, in which basic physical
principles can be profitably employed. This study connects two different
domains: the fast motion of macroscopic bodies in resistant media and the
interaction of charged subatomic particles with matter at high energies, which
furnish the two limit cases of the problem of penetrating projectiles of
different sizes. These limit cases actually have overlapping applications; for
example, in space physics and technology. The intermediate or mesoscopic domain
finds application in atom cluster implantation technology. Here it is shown
that the penetration of fast nano-projectiles is ruled by a slightly modified
Newton's inertial quadratic force, namely, $F \sim v^{2-\beta}$, where $\beta$
vanishes as the inverse of projectile diameter. Factors essential to
penetration depth are ratio of projectile to medium density and projectile
shape. | 1705.02337v2 |
2017-07-07 | Resistance distance criterion for optimal slack bus selection | We investigate the dependence of transmission losses on the choice of a slack
bus in high voltage AC transmission networks. We formulate a transmission loss
minimization problem in terms of slack variables representing the additional
power injection that each generator provides to compensate the transmission
losses. We show analytically that for transmission lines having small,
homogeneous resistance over reactance ratios ${r/x\ll1}$, transmission losses
are generically minimal in the case of a unique \textit{slack bus} instead of a
distributed slack bus. For the unique slack bus scenario, to lowest order in
${r/x}$, transmission losses depend linearly on a resistance distance based
indicator measuring the separation of the slack bus candidate from the rest of
the network. We confirm these results numerically for several IEEE and Pegase
testcases, and show that our predictions qualitatively hold also in the case of
lines having inhomogeneous ${r/x}$ ratios, with optimal slack bus choices
reducing transmission losses by ${10}\%$ typically. | 1707.02845v1 |
2017-07-18 | Umklapp scattering as the origin of $T$-linear resistivity in the normal state of high-$T_c$ cuprate superconductors | The high-temperature normal state of the unconventional cuprate
superconductors has resistivity linear in temperature $T$, which persists to
values well beyond the Mott-Ioffe-Regel upper bound. At low-temperature, within
the pseudogap phase, the resistivity is instead quadratic in $T$, as would be
expected from Fermi liquid theory. Developing an understanding of these normal
phases of the cuprates is crucial to explain the unconventional
superconductivity. We present a simple explanation for this behavior, in terms
of umklapp scattering of electrons. This fits within the general picture
emerging from functional renormalization group calculations that spurred the
Yang-Rice-Zhang ansatz: umklapp scattering is at the heart of the behavior in
the normal phase. | 1707.05666v4 |
2018-08-29 | Resistivity of high pressure phosphorus phases | Simple cubic (sc) black phosphorus (denoted BP), stable at P>10GPa, seems an
ordinary metal. It has electron-phonon-driven superconductivity with Tc 5-10 K.
The A17 phase, stable at atmospheric pressure, has a narrow gap, becomes
semimetallic at P=1 GPa, and has a smooth transition to topological metal
behavior at P ~ 5 GPa. The A7 phase, stable for 5<P<10 GPa, is metallic,
superconducting, and less conventional than the sc phase. Some insights are
extracted from analysis of resistivity versus temperature at various pressures.
A surprising order-of-magnitude disagreement between theory and experiment is
discussed. | 1808.09914v2 |
2019-12-17 | Defects Mitigation in Resistive Crossbars for Analog Vector Matrix Multiplication | With storage and computation happening at the same place, computing in
resistive crossbars minimizes data movement and avoids the memory bottleneck
issue. It leads to ultra-high energy efficiency for data-intensive
applications. However, defects in crossbars severely affect computing accuracy.
Existing solutions, including re-training with defects and redundant designs,
but they have limitations in practical implementations. In this work, we
introduce row shuffling and output compensation to mitigate defects without
re-training or redundant resistive crossbars. We also analyzed the coupling
effects of defects and circuit parasitics. Moreover, We study different
combinations of methods to achieve the best trade-off between cost and
performance. Our proposed methods could rescue up to 10% of defects in
ResNet-20 application without performance degradation. | 1912.07829v1 |
2012-03-08 | CensorSpoofer: Asymmetric Communication with IP Spoofing for Censorship-Resistant Web Browsing | A key challenge in censorship-resistant web browsing is being able to direct
legitimate users to redirection proxies while preventing censors, posing as
insiders, from discovering their addresses and blocking them. We propose a new
framework for censorship-resistant web browsing called {\it CensorSpoofer} that
addresses this challenge by exploiting the asymmetric nature of web browsing
traffic and making use of IP spoofing. CensorSpoofer de-couples the upstream
and downstream channels, using a low-bandwidth indirect channel for delivering
outbound requests (URLs) and a high-bandwidth direct channel for downloading
web content. The upstream channel hides the request contents using
steganographic encoding within email or instant messages, whereas the
downstream channel uses IP address spoofing so that the real address of the
proxies is not revealed either to legitimate users or censors. We built a
proof-of-concept prototype that uses encrypted VoIP for this downstream channel
and demonstrated the feasibility of using the CensorSpoofer framework in a
realistic environment. | 1203.1673v2 |
2012-03-11 | Ultrasound and Temperature Study of Non-Equilibrium Phase Transitions in Surface-Bound Liquid Layers | The present research deals with the registration and study of temperature and
ultrasound parameters of non-equilibrium phase transitions occurring in the
layer "liquid-solid surface" in the process of slow heating and cooling of the
medium. Different resistive sensors have been used for taking measurements. As
a result there has been discovered a periodic stepped dependence of the
registered temperature with jumps ~7.5-13 K in water, water solutions and other
liquids. We have studied the conditions under which the stepped temperature
dependence of the resistive sensors indications is synchronous to the resonance
frequency variations of the liquid volume limited by the surface of the axial
piezoelectric resonator. The experiments showed that for studying temperature
transitions and ultrasound phase velocity variations the following conditions
are required: ac field in the area of the liquid surface layer. Assumed cause
of the temperature jumps occurrence is high heat conduction and heat capacity
of the surface-bound layer, causing local temperature variations on the surface
of the resistive sensor in the process of evolution of the two-dimensional
crystal liquid structure. Investigation of non-equilibrium transitions of the
surface-bound liquid layer may be of interest for studying molecular complexes
of liquid media, as well as cellular structures of living systems. | 1203.2333v1 |
2012-06-11 | Enhanced Dissipation Rate of Magnetic Field in Striped Pulsar Winds by the Effect of Turbulence | In this letter we report on turbulent acceleration of the dissipation of
magnetic field in the postshock re- gion of a Poynting flux-dominated flow,
such as the Crab pulsar wind nebula. We have performed two- dimensional
resistive relativistic magnetohydrodynamics simulations of subsonic turbulence
driven by the Richtmyer-Meshkov instability at the shock fronts of the Poynting
flux-dominated flows in pulsar winds. We find that turbulence stretches current
sheets which substantially enhances the dissipation of magnetic field, and that
most of the initial magnetic field energy is dissipated within a few
eddy-turnover times. We also develop a simple analytical model for turbulent
dissipation of magnetic field that agrees well with our simulations. The
analytical model indicates that the dissipation rate does not depend on
resistivity even in the small resistivity limit. Our findings can possibly
alleviate the {\sigma}-problem in the Crab pulsar wind nebulae. | 1206.2087v1 |
2015-04-22 | Determination of the Riemann modulus and sheet resistivity by a six-point generalization of the van der Pauw method | Six point generalization of the van der Pauw method is presented. The method
is applicable for two dimensional homogeneous systems with an isolated hole. A
single measurement performed on the contacts located arbitrarily on the sample
edge allows to determine the specific resistivity and a dimensionless parameter
related to the hole, known as the Riemann modulus. The parameter is invariant
under conformal mappings of the sample shape. The hole can be regarded as a
high resistivity defect. Therefore the method can be applied for experimental
determination of the sample inhomogeneity. | 1504.05763v1 |
2015-07-30 | Field-dependent surface resistance of a superconducting RF cavity caused by surface impurity | Q-slope issue, which is caused by the field dependent surface resistance,
puzzled people for a long time in SRF fields. In this paper, we related the
Q-slope with surface treatments; and proposed a surface-impurity model to
explain the field-dependent of surface resistance of SRF cavities. Eighteen
cavity-test results have been analyzed to examine the model. These cavities
were treated by different recipes: Nitrogen-doping; BCP and HF-rinsing; EP with
120{\deg}C baking; and EP without 120{\deg}C baking. The performance of these
cavities, which is normally represented by cavity quality factor versus
accelerating gradient or surface magnetic field curves (Q0 vs. Eacc or Q0 vs.
B), has included all types of Q-slope, such as Low-field Q-slope, Medium-field
Q-slope, and Anti-Q-slope. The data fittings are quite successful; the fitting
results will be shown. The model can be used to evaluate the effectiveness of
the surface treatments. At last, the paper discussed the way to build a high-Q
high-gradient SRF cavity. | 1507.08704v2 |
2016-09-29 | Jet formation in solar atmosphere due to magnetic reconnection | Using numerical simulations, we show that jets with features of type II
spicules and cold coronal jets corresponding to temperatures $10^{4}$ K can be
formed due to magnetic reconnection in a scenario in presence of magnetic
resistivity. For this we model the low chromosphere-corona region using the C7
equilibrium solar atmosphere model and assuming Resistive MHD rules the
dynamics of the plasma. The magnetic filed configurations we analyze correspond
to two neighboring loops with opposite polarity. The separation of the loops'
feet determines the thickness of a current sheet that triggers a magnetic
reconnection process, and the further formation of a high speed and sharp
structure. We analyze the cases where the magnetic filed strength of the two
loops is equal and different. In the first case, with a symmetric configuration
the spicules raise vertically whereas in an asymmetric configuration the
structure shows an inclination. With a number of simulations carried out under
a 2.5D approach, we explore various properties of excited jets, namely, the
morphology, inclination and velocity. The parameter space involves magnetic
field strength between 20 and 40 G, and the resistivity is assumed to be
uniform with a constant value of the order $10^{-2}\Omega\cdot m$ | 1609.09422v1 |
2018-07-03 | Design of a New Stream Cipher: PALS | In this paper, a new stream cipher is designed as a clock-controlled one, but
with a new mechanism of altering steps based on system theory in such a way
that the structures used in it are resistant to conventional attacks. Our
proposed algorithm (PALS) uses the main key with the length of 256 bits and a
32-bit message key. The most important criteria considered in designing the
PALS are resistance to known attacks, maximum period, high linear complexity,
and good statistical properties. As a result, the output keystream is very
similar to the perfectly random sequences and resistant to conventional attacks
such as correlation attacks, algebraic attack, divide & conquer attack,
time-memory tradeoff attack and AIDA/cube attacks. The base structure of the
PALS is a clock-controlled combination generator with memory and we obtained
all the features according to design criteria with this structure. PALS can be
used in many applications, especially in financial cryptography due to its
proper security features | 1807.01115v2 |
2018-12-19 | Coherent vs incoherent transport in holographic strange insulators | Holographic strange metals are known to have a power law resistivity rising
with temperature, which is reminiscent of the strange metal phases in condensed
matter systems. In some holographic models, however, the exponent of the power
law in the resistivity can be negative. In this case one encounters phases with
diverging resistivity at zero temperature: holographic strange insulators.
These states arise as a result of translational symmetry breaking in the
system, which can either be strong explicit and relevant in the IR, or
spontaneous, but pinned by a small explicit source. In some regards, one can
associate these two classes to the normal band insulators due to the strong
ionic potential, and Mott insulator due to the commensurate lock in of the
charge density wave.
We study different features of these classes on the explicit example of a
holographic helical model with homogeneous Bianchy VII type translational
symmetry breaking, and uncover the main mechanisms underlying transport in
these two cases. We find that while transport in the explicit relevant case is
governed by the incoherent conductivity, in the pinned spontaneous case the
leading contribution comes from the coherent part. | 1812.08132v2 |
2019-01-21 | Possible pressure-induced topological quantum phase transition in the nodal line semimetal ZrSiS | ZrSiS has recently gained attention due to its unusual electronic properties:
nearly perfect electron-hole compensation, large, anisotropic
magneto-resistance, multiple Dirac nodes near the Fermi level, and an extremely
large range of linear dispersion of up to 2 eV. We have carried out a series of
high pressure electrical resistivity measurements on single crystals of ZrSiS.
Shubnikov-de Haas measurements show two distinct oscillation frequencies. For
the smaller orbit, we observe a change in the phase of 0.5, which occurs
between 0.16 - 0.5 GPa. This change in phase is accompanied by an abrupt
decrease of the cross-sectional area of this Fermi surface. We attribute this
change in phase to a possible topological quantum phase transition. The phase
of the larger orbit exhibits a Berry phase of pi and remains roughly constant
up to 2.3 GPa. Resistivity measurements to higher pressures show no evidence
for pressure-induced superconductivity to at least 20 GPa. | 1901.07043v1 |
2019-06-19 | Comment on arXiv:1807.08572: a plausible explanation of the giant diamagnetism found in Au-Ag nanostructures | In a recent comment (arXiv:1906.05742) on the preprint (arXiv:1807.08572)
entitled "Coexistence of Diamagnetism and Vanishingly Small Electrical
Resistance at Ambient Temperature and Pressure in Nanostructures", it is
pointed out that the reduction of the four-probe resistance ($R_{4P}$) to zero
value is accompanied by a rise in the two probe resistance ($R_{2P}$) in the
same temperature range. This curious correlation between $R_{4P}$ and $R_{2P}$
is said to be pointing towards a non-superconducting "conductance percolation"
transition (rather than "percolating superconducting transition" as proposed in
the revised version of arxiv:1807.08572). The explanation offered in preprint
arXiv:1906.05742 is quite reasonable, but the author leaves open the question
of giant diamagnetism. In this short comment I suggest a plausible cause of the
giant diamagnetism found in nanostructures. It could be due to gapped
electronic energy spectrum of nanoparticles which is due to quantum confinement
effects, and that suppresses the electronic scattering mechanism leading to a
very high value of Langevin diamagnetism. | 1906.08128v1 |
2019-10-05 | Resistivity anisotropy of quantum Hall stripe phases | Quantum Hall stripe phases near half-integer filling factors $\nu \ge 9/2$
were predicted by Hartree-Fock (HF) theory and confirmed by discoveries of
giant resistance anisotropies in high-mobility two-dimensional electron gases.
A theory of such anisotropy was proposed by MacDonald and Fisher, although they
used parameters whose dependencies on the filling factor, electron density, and
mobility remained unspecified. Here, we fill this void by calculating the
hard-to-easy resistivity ratio as a function of these three variables.
Quantitative comparison with experiment yields very good agreement which we
view as evidence for the "plain vanilla" smectic stripe HF phases. | 1910.02260v3 |
2020-11-27 | Pinning, flux flow resistivity and anisotropy of Fe(Se,Te) thin films from microwave measurements through a bitonal dielectric resonator | We report on the anisotropy of the vortex motion surface impedance of a \fst
thin film grown on a CaF$_2$ substrate. The dependence on the magnetic field
intensity up to 1.2 T and direction, both parallel and perpendicular to the
sample $c$-axis, was explored at fixed temperature at two distinct frequencies,
$\sim16\;$GHz and $\sim27\;$GHz, by means of bitonal dielectric resonator. The
free flux flow resistivity $\rho_{ff}$ was obtained by exploiting standard
models for the high frequency dynamics, whereas the angle dependence was
studied in the framework of the well known and widely used
Blatter-Geshkenbein-Larkin (BGL) scaling theory for anistropic superconductors.
Excellent agreement with the scaling law prescription by the fluxon flux flow
resistivity was obtained. From the scaling analysis, a low-field mass
anisotropy $\sim1.8$ was obtained, well within the value ranges reported in
literature. The angular dependence of the pinning constant suggests that
pinning is dominated by random, isotropic point pins, consistently with
critical current density measurements. | 2011.13819v1 |
2020-12-17 | Low temperature $T$-linear resistivity due to umklapp scattering from a critical mode | We consider the transport properties of a model of fermions scattered by a
critical bosonic mode. The mode is overdamped and scattering is mainly in the
forward direction. Such a mode appears at the quantum critical point for a
electronic nematic phase transition, and in gauge theories for a U(1) spin
liquid. It leads to a short fermion life-time, violating Landau's criterion for
a Fermi liquid. In spite of this, transport can be described by a Boltzmann
equation. We include momentum relaxation by umklapp scattering, supplemented by
weak impurity scattering. We find that above a very low temperature which
scales with $\Delta_q^3$, where $\Delta_q$ is the minimum umklapp scattering
vector, the resistivity is linear in $T$ with a coefficient which is
independent of the amount of disorder. We compare the relaxation time
approximation with an exact numerical solution of the Boltzmann equation.
Surprisingly we find that unlike the resistivity, the Hall Coefficient strongly
deviates from the relaxation time approximation and shows a strong reduction
with increasing temperature. We comment on possible comparisons with
experiments on high $T_c$ Cuprates. | 2012.09339v1 |
2021-06-08 | Transport in the 2D Fermi-Hubbard Model: Lessons from Weak Coupling | We use quantum kinetic theory to calculate the thermoelectric transport
properties of the 2D single band Fermi-Hubbard model in the weak coupling
limit. For generic filling, we find that the high-temperature limiting
behaviors of the electrical ($\sim T$) and thermal ($\sim T^2$) resistivities
persist down to temperatures of order the hopping matrix element $T\sim t$,
almost an order of magnitude below the bandwidth. At half filling, perfect
nesting leads to anomalous low temperature scattering and nearly $T$-linear
electrical resistivity at all temperatures. We hypothesize that the $T$-linear
resistivity observed in recent cold atom experiments is continuously connected
to this weak coupling physics and suggest avenues for experimental
verification. We find a number of other novel thermoelectric results, such as a
low-temperature Wiedemann-Franz law with Lorenz coefficient $5\pi^2/36$. | 2106.04479v2 |
2021-08-12 | Spatio-temporal evolution of resistance state in simulated memristive networks | Originally studied for their suitability to store information compactly,
memristive networks are now being analysed as implementations of neuromorphic
circuits. An extremely high number of elements is thus mandatory. To surpass
the limited achievable connectivity - due to the featuring size - exploiting
self-assemblies has been proposed as an alternative, in turn posing more
challenges. In an attempt for offering insight on what to expect when
characterizing the collective electrical response of switching assemblies, in
this work, networks of memristive elements are simulated. Collective electrical
behaviour and maps of resistance states are characterized upon different
electrical stimuli. By comparing the response of homogeneous and heterogeneous
networks, we delineate differences that might be experimentally observed when
the number of memristive units is scaled up and disorder arises as an
inevitable feature. | 2108.05830v2 |
2021-12-15 | Gaining Outlier Resistance with Progressive Quantiles: Fast Algorithms and Theoretical Studies | Outliers widely occur in big-data applications and may severely affect
statistical estimation and inference. In this paper, a framework of
outlier-resistant estimation is introduced to robustify an arbitrarily given
loss function. It has a close connection to the method of trimming and includes
explicit outlyingness parameters for all samples, which in turn facilitates
computation, theory, and parameter tuning. To tackle the issues of nonconvexity
and nonsmoothness, we develop scalable algorithms with implementation ease and
guaranteed fast convergence. In particular, a new technique is proposed to
alleviate the requirement on the starting point such that on regular datasets,
the number of data resamplings can be substantially reduced. Based on combined
statistical and computational treatments, we are able to perform nonasymptotic
analysis beyond M-estimation. The obtained resistant estimators, though not
necessarily globally or even locally optimal, enjoy minimax rate optimality in
both low dimensions and high dimensions. Experiments in regression,
classification, and neural networks show excellent performance of the proposed
methodology at the occurrence of gross outliers. | 2112.08471v3 |
2022-02-28 | Structure from Voltage | Effective resistance (ER) is an attractive way to interrogate the structure
of graphs. It is an alternative to computing the eigen-vectors of the graph
Laplacian. Graph laplacians are used to find low dimensional structures in high
dimensional data. Here too, ER based analysis has advantages over eign-vector
based methods. Unfortunately Von Luxburg et al. (2010) show that, when vertices
correspond to a sample from a distribution over a metric space, the limit of
the ER between distant points converges to a trivial quantity that holds no
information about the structure of the graph. We show that by using scaling
resistances in a graph with $n$ vertices by $n^2$, one gets a meaningful limit
of the voltages and of effective resistances. We also show that by adding a
"ground" node to a metric graph one gets a simple and natural way to compute
all of the distances from a chosen point to all other points. | 2203.00063v2 |
2022-03-31 | Structural Phase Transition and Possible Valence Instability of Ce$-4f$ Electron Induced by Pressure in CeCoSi | X-ray powder diffraction and electrical resistivity measurements were
performed on the tetragonal compound CeCoSi under pressure to elucidate the
phase boundary of the pressure-induced structural transition and the change in
the 4$f$ electronic state. The temperature-pressure phase diagram has been
determined from the shift of the Bragg peaks and from the anomaly in the
resistivity. The critical pressure, $P_{\rm s}$ $\sim$ 4.9 GPa at 300 K,
decreases to $P_{\rm s}$ $\sim$ 3.6 GPa at 10 K. The decrease of $P_{\rm s}$ is
due not only to the decrease in volume of the unit cell but also to an
anisotropic shrinkage by cooling. When crossing the boundary to the
high-pressure phase, the resistivity shows a significant drop to exhibit a
metallic temperature dependence. The results of this study strongly suggest
that the structural phase transition can be ascribed to valence instability of
Ce-$4f$ electron. | 2203.16817v1 |
2022-05-05 | MMINR: Multi-frame-to-Multi-frame Inference with Noise Resistance for Precipitation Nowcasting with Radar | Precipitation nowcasting based on radar echo maps is essential in
meteorological research. Recently, Convolutional RNNs based methods dominate
this field, but they cannot be solved by parallel computation resulting in
longer inference time. FCN based methods adopt a multi-frame-to-single-frame
inference (MSI) strategy to avoid this problem. They feedback into the model
again to predict the next time step to get multi-frame nowcasting results in
the prediction phase, which will lead to the accumulation of prediction errors.
In addition, precipitation noise is a crucial factor contributing to high
prediction errors because of its unpredictability. To address this problem, we
propose a novel Multi-frame-to-Multi-frame Inference (MMI) model with Noise
Resistance (NR) named MMINR. It avoids error accumulation and resists
precipitation noise\'s negative effect in parallel computation. NR contains a
Noise Dropout Module (NDM) and a Semantic Restore Module (SRM). NDM
deliberately dropout noise simple yet efficient, and SRM supplements semantic
information of features to alleviate the problem of semantic information
mistakenly lost by NDM. Experimental results demonstrate that MMINR can attain
competitive scores compared with other SOTAs. The ablation experiments show
that the proposed NDM and SRM can solve the aforementioned problems. | 2205.02457v1 |
2022-05-12 | Tutorial: Analog Matrix Computing (AMC) with Crosspoint Resistive Memory Arrays | Matrix computation is ubiquitous in modern scientific and engineering fields.
Due to the high computational complexity in conventional digital computers,
matrix computation represents a heavy workload in many data-intensive
applications, e.g., machine learning, scientific computing, and wireless
communications. For fast, efficient matrix computations, analog computing with
resistive memory arrays has been proven to be a promising solution. In this
Tutorial, we present analog matrix computing (AMC) circuits based on crosspoint
resistive memory arrays. AMC circuits are able to carry out basic matrix
computations, including matrix multiplication, matrix inversion, pseudoinverse
and eigenvector computation, all with one single operation. We describe the
main design principles of the AMC circuits, such as local/global or
negative/positive feedback configurations, with/without external inputs.
Mapping strategies for matrices containing negative values will be presented.
The underlying requirements for circuit stability will be described via the
transfer function analysis, which also defines time complexity of the circuits
towards steady-state results. Lastly, typical applications, challenges, and
future trends of AMC circuits will be discussed. | 2205.05853v1 |
2022-08-17 | Silicon sensors with resistive read-out: Machine Learning techniques for ultimate spatial resolution | Resistive AC-coupled Silicon Detectors (RSDs) are based on the Low Gain
Avalanche Diode (LGAD) technology, characterized by a continuous gain layer,
and by the innovative introduction of resistive read-out. Thanks to a novel
electrode design aimed at maximizing signal sharing, RSD2, the second RSD
production by Fondazione Bruno Kessler (FBK), achieves a position resolution on
the whole pixel surface of about 8 $\mu m$ for 200-$\mu m$ pitch. RSD2 arrays
have been tested using a Transient Current Technique setup equipped with a
16-channel digitizer, and results on spatial resolution have been obtained with
machine learning algorithms. | 2208.08294v2 |
2022-09-27 | Clean-limit superconductivity in Im-3m H3S synthesized from sulfur and hydrogen donor ammonia borane | We present detailed studies of the superconductivity in high-pressure H3S.
X-ray diffraction measurements show that cubic Im-3m H3S was synthesized from
elemental sulfur and hydrogen donor ammonia borane (NH3BH3). Our electrical
transport measurements confirm superconductivity with a transition temperature
Tc = 197 K at 153 GPa. From the analysis of both the normal state resistivity
and the slope of the critical field, we conclude that the superconductivity is
described by clean-limit behaviour. A significant broadening of the resistive
transition in finite magnetic field is found, as expected for superconductors.
We identify a linear temperature-over-field scaling of the resistance at the
superconducting transition which is not described by existing theories. | 2209.13299v1 |
2022-12-02 | Hybrid Tunable Magnet Actuator: Modeling and Design | Reluctance actuators are preferred for high-precision applications. Due to
resistive losses in the coils, the accuracy of this type of actuator will
reduce in quasi-static operation mode within a vacuum environment. By using
soft permanent magnets whose magnetization states are in-situ tuned, no
constant power is needed to create a force and thereby the resistive losses
will reduce. In this paper, a new tuning method is investigated in order to
reduce the resistive losses. By using a history-dependent and non-linear
hysteresis model, a more efficient tuning algorithm is designed. Besides this,
the position accuracy and control simplicity of a variable reluctance tunable
magnet actuator are improved by linearizing the non-linear force-flux
relationship. This is achieved by using bias fluxes generated by hard permanent
magnets. | 2212.01242v1 |
2022-12-14 | Magnetic field evolution and reconnection in low resistivity plasmas | The mathematics and physics of each of the three aspects of magnetic field
evolution -- topology, energy, and helicity -- is remarkably simple and clear.
When the resistivity $\eta$ is small compared to an imposed evolution, $a/v$,
timescale, which means $R_m\equiv\mu_0va/\eta>>1$, magnetic field line chaos
dominates the evolution of field-line topology in three-dimensional systems.
Chaos has no direct role in the dissipation of energy. A large current density,
$j_\eta\equiv vB/\eta$, is required for energy dissipation to be on a
comparable time scale to the topological evolution. Nevertheless, chaos plus
Alfv\'en wave damping explain why both timescales tend to be approximately an
order of magnitude longer than the evolution timescale $a/v$. Magnetic helicity
is injected onto tubes of field lines when boundary flows have vorticity. Chaos
can spread but not destroy magnetic helicity. Resistivity has a negligible
effect on helicity accumulation when $R_m>>1$. Helicity accumulates within a
tube of field lines until the tube erupts and moves far from its original
location. | 2212.07487v3 |
2023-03-30 | Partial condensation of mobile excitons in graphene multilayers | At a large displacement field, in rhomboedral and Bernal-stacked graphene a
normal paramagnetic state transitions to a correlated state. Recent experiments
showed that such systems have several phase transitions as a function of the
carrier density. The phase adjacent to a paramagnetic state has anomalously
high resistance and reduced degeneracy of the Fermi sea. We show that both
phenomena can be explained through a concept of partial intervalley exciton
condensation: a fraction of particles condenses into excitons, and another
forms an intervalley coherent Fermi liquid. The exciton part of the system do
not contribute to the electrical current thus increasing the resistance. Within
this paradigm, the increase in the resistance has entirely geometrical origin.
We check validity of the phenomenological theory through numerical
calculations. We also show that the quantum oscillation data should not be very
different between the partial excitonic state and the intervalley coherent
states suggested by other authors. Further, we suggest STM/AFM or Raman
spectroscopy to have a conclusive evidence for the occurrence of the partial
exciton condensation that we suggest in this paper. | 2303.17350v1 |
2023-05-11 | Dendritic Computation through Exploiting Resistive Memory as both Delays and Weights | Biological neurons can detect complex spatio-temporal features in spiking
patterns via their synapses spread across across their dendritic branches. This
is achieved by modulating the efficacy of the individual synapses, and by
exploiting the temporal delays of their response to input spikes, depending on
their position on the dendrite. Inspired by this mechanism, we propose a
neuromorphic hardware architecture equipped with multiscale dendrites, each of
which has synapses with tunable weight and delay elements. Weights and delays
are both implemented using Resistive Random Access Memory (RRAM). We exploit
the variability in the high resistance state of RRAM to implement a
distribution of delays in the millisecond range for enabling spatio-temporal
detection of sensory signals. We demonstrate the validity of the approach
followed with a RRAM-aware simulation of a heartbeat anomaly detection task. In
particular we show that, by incorporating delays directly into the network, the
network's power and memory footprint can be reduced by up to 100x compared to
equivalent state-of-the-art spiking recurrent networks with no delays. | 2305.06941v2 |
2023-07-26 | $N_{\rm eff}$ constraints on light mediators coupled to neutrinos: the dilution-resistant effect | We investigate the impact of new light particles, carrying significant energy
in the early universe after neutrino decoupling, on the cosmological effective
relativistic neutrino species, $N_{{\rm eff}}$. If the light particles are
produced from decoupled neutrinos, $N_{{\rm eff}}$ is predominantly modified
through the dilution-resistant effect. This effect arises because the energy
stored in the mass of new particles is less diluted than the photon and
neutrino energy as the universe expands. Our study comprehensively explores
this effect, deriving $N_{{\rm eff}}$ constraints on the couplings of light
mediators with neutrinos, encompassing both scalar and vector mediators. We
find that the dilution-resistant effect can increase $N_{{\rm eff}}$ by 0.118
and 0.242 for scalar and vector mediators, respectively. These values can be
readily reached by forthcoming CMB experiments. Upon reaching these levels,
future $N_{{\rm eff}}$ constraints on the couplings will be improved by many
orders of magnitude. | 2307.13967v2 |
2023-08-08 | First order transition in Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O ($0.9<x<1.1$) containing Cu$_2$S | Lee et al. reported that the compound LK99, with a chemical formula of
Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O ($0.9<x<1.1$), exhibits room-temperature
superconductivity under ambient pressure. In this study, we investigated the
transport and magnetic properties of pure Cu$_2$S and LK-99 containing Cu$_2$S.
We observed a sharp superconducting-like transition and a thermal hysteresis
behavior in the resistivity and magnetic susceptibility. However, we did not
observe zero-resistivity below the transition temperature. We argue that the
so-called superconducting behavior in LK-99 is most likely due to a reduction
in resistivity caused by the first order structural phase transition of Cu$_2$S
at around 385 K, from the $\beta$ phase at high temperature to the $\gamma$
phase at low temperature. | 2308.04353v1 |
2023-11-19 | Small-area Portable Resistive Plate Chambers for Muography | Muography is finding applications in various domains such as volcanology,
archaeology, civil engineering, industry, mining, and nuclear waste surveys. To
simplify transportation and installation in remote locations after laboratory
testing, a fully portable and autonomous muon telescope based on Resistive
Plate Chambers (RPCs) is being developed. Two glass-RPC prototypes have been
created, sharing the same design goals but with different detector parameters,
and comparative studies are ongoing. Drawing from prototype experience, a
double-gap RPC with advanced features and improved spatial resolution is
constructed. Resistive electrodes are produced manually, and a new data
acquisition board is currently undergoing calibration. The results on prototype
performance, readout board comparisons and the technical progress on the
double-gap RPC are presented. | 2311.11451v1 |
2023-12-21 | Quantum Transport and Spectroscopy of Two-dimensional Perovskite/Graphene Interfaces | Quantum transport properties in molecularly thin perovskite/graphene
heterostructure are experimentally investigated by Shubnikov-de Hass (SdH)
oscillation and photo-resistance spectroscopy. We find an efficient charge
transfer between the perovskite nanosheets and graphene, with a high hole
concentration in graphene of up to $\rm \sim 2.8 \times 10^{13}\ cm^{-2}$. The
perovskite layer also increases Fermi velocity lowering the effective mass of
graphene from expected $\rm \sim 0.12\ m_e$ to $\rm \sim 0.08\ m_e$. Combining
magneto-resistance and density functional theory calculations, we find that the
carrier density in graphene significantly depends on the perovskite termination
at the interface, affecting the charge transfer process and leading to a
coexistence of regions with different doping. We also investigate the
photo-response of the SdH oscillation under illumination. Using
photo-resistance spectroscopy, we find evidence of photo-assisted transport
across the perovskite layer between two graphene electrodes mediated by hot
carriers in perovskite. Our results provide a picture to understand the
transport behavior of 2D perovskite/graphene heterostructure and a reference
for the controlled design of interfaces in perovskite optoelectronic devices. | 2312.13956v1 |
2023-12-23 | A Hybrid Image Encryption Scheme based on Chaos and a DPA-Resistant Sbox | Image encryption is one of the most common and effective methods to secure
digital images. Recently, Khalid M. Hosny presented an image encryption scheme
based on 6D hyper chaotic mapping and Q-Fibonacci matrix, which, despite its
remarkable theoretical and practical properties, has several weaknesses,
including inaccuracy of black image encryption, inappropriate white image
encryption (improper entropy parameters, correlation, chi-square test,
histogram, UACI, and NPCR), weak keys, inappropriate key usage. In this paper,
based on Khaled Hosny's design, a new effective design is presented that has
improved encryption security and efficiency. In addition, in the proposed
design, a secure key and a substitution box with a high degree of transparency
order, which is resistant to DPA attacks, have been added. Also, a method to
improve transferring chaos parameters is also proposed. The test results show
the improvement of the resistance of the proposed design against the common
attacks of image encryption schemes and improvement in bandwidth consumption.
Also it has been shown that the proposed scheme has produced better results in
terms of both security and efficiency compared to other similar new schemes. | 2312.15280v1 |
2024-02-02 | Constructing 100 MΩ and 1 GΩ Resistance Standards via Star-Mesh Transformations | A recent mathematical framework for optimizing resistor networks to achieve
values in the M{\Omega} through G{\Omega} levels was employed for two specific
cases. Objectives here include proof of concept and identification of possible
apparatus limitations for future experiments involving graphene-based quantum
Hall array resistance standards. Using fractal-like, or recursive, features of
the framework allows one to calculate and implement network designs with
substantially lower-valued resistors. The cases of 100 M{\Omega} and 1
G{\Omega} demonstrate that, theoretically, one would not need more than 100
quantum Hall elements to achieve these high resistances. | 2402.01496v1 |
2024-02-07 | Stochastic modeling of Random Access Memories reset transitions | Resistive Random Access Memories (RRAMs) are being studied by the industry
and academia because it is widely accepted that they are promising candidates
for the next generation of high density nonvolatile memories. Taking into
account the stochastic nature of mechanisms behind resistive switching, a new
technique based on the use of functional data analysis has been developed to
accurately model resistive memory device characteristics. Functional principal
component analysis (FPCA) based on Karhunen-Loeve expansion is applied to
obtain an orthogonal decomposition of the reset process in terms of
uncorrelated scalar random variables. Then, the device current has been
accurately described making use of just one variable presenting a modeling
approach that can be very attractive from the circuit simulation viewpoint. The
new method allows a comprehensive description of the stochastic variability of
these devices by introducing a probability distribution that allows the
simulation of the main parameter that is employed for the model implementation.
A rigorous description of the mathematical theory behind the technique is given
and its application for a broad set of experimental measurements is explained. | 2402.05209v1 |
2024-02-16 | Coherent states in microwave-induced resistance oscillations and zero resistance states | We investigate irradiated high-mobility two-dimensional electron systems
(2DES) under low or moderated magnetic fields. These systems present
microwave-induced magnetoresistance oscillations (MIRO) which, as we
demonstrate, reveal the presence of coherent states of the quantum harmonic
oscillator. We also show that the principle of minimum uncertainty of coherent
states is at the heart of MIRO and zero resistance states (ZRS). Accordingly,
we are able to explain, based on coherent states, important experimental
evidence of these photo-oscillations. Such as their physical origin, their
periodicity with the inverse of the magnetic field and their peculiar
oscillations minima and maxima positions in regards of the magnetic field.
Thus, remarkably enough, we come to the conclusion that 2DES, under low
magnetic fields, become a system of quasiclassical states or coherent states
and MIRO would be the smoking gun of the existence of these peculiar states is
these systems. | 2402.11002v1 |
2024-02-26 | Improving the JPEG-resistance of Adversarial Attacks on Face Recognition by Interpolation Smoothing | JPEG compression can significantly impair the performance of adversarial face
examples, which previous adversarial attacks on face recognition (FR) have not
adequately addressed. Considering this challenge, we propose a novel
adversarial attack on FR that aims to improve the resistance of adversarial
examples against JPEG compression. Specifically, during the iterative process
of generating adversarial face examples, we interpolate the adversarial face
examples into a smaller size. Then we utilize these interpolated adversarial
face examples to create the adversarial examples in the next iteration.
Subsequently, we restore the adversarial face examples to their original size
by interpolating. Throughout the entire process, our proposed method can smooth
the adversarial perturbations, effectively mitigating the presence of
high-frequency signals in the crafted adversarial face examples that are
typically eliminated by JPEG compression. Our experimental results demonstrate
the effectiveness of our proposed method in improving the JPEG-resistance of
adversarial face examples. | 2402.16586v1 |
2024-02-23 | Accelerating Dimensionality Reduction in Wave-Resistance Problems through Geometric Operators | Reducing the dimensionality and uncertainty of design spaces is a key
prerequisite for shape optimisation in computationally intensive fluid
problems. However, running these analyses at an offline stage itself poses a
computationally demanding task. In this work, we propose a unique framework for
the inexpensive implementation of sensitivity analyses for reducing the
dimensionality of the design space in wave-resistance problems. At the heart of
our approach is the formulation of a geometric operator that leverages, via
high-order geometric moments, the underlying connection between geometry and
physics, specifically the wave-resistance coefficient ($C_w$), of ships using
the slender body theory based on the well-known Vossers' integral. The
resulting geometric operator is computationally inexpensive yet
physics-informed and can act as a geometry-based surrogate to drive parametric
sensitivities. To analytically demonstrate the capability of the proposed
approach, we use a well-known benchmark geometry, namely, the modified Wigley
hull. Its simple analytical formulation allows for closed expressions of the
geometric operators and exploration of computational domains that would
otherwise be inaccessible. In this context, the proposed geometric operator
outperforms existing similar approaches by achieving 100% similarity with $C_w$
at a fraction of the computational cost. | 2403.06990v1 |
2024-03-14 | Electronic diffusion in a normal state of high-Tc cuprate YBa$_2$Cu$_3$O$_{6+x}$ | The bad metallic phase with resistivity above the Mott-Ioffe-Regel limit,
which appears also in cuprate superconductors, was recently understood by cold
atom and computer simulations of the Hubbard model via charge susceptibility
and charge diffusion constant. However, since reliable simulations can be
typically done only at temperatures above the experimental temperatures, the
question for cuprate superconductors is still open. This paper addresses this
question by resorting to heat transport, which allows for the estimate of
electronic diffusion and it further combines it with the resistivity to
estimate the charge susceptibility. The doping and temperature dependencies of
diffusion constant and charge susceptibilities are shown and discussed for two
samples of YBa$_2$Cu$_3$O$_{6+x}$. Results indicate strongly incoherent
transport, mean free path corresponding to the Mott-Ioffe-Regel limit for the
underdoped sample at temperatures above ~200 K and significant effect of the
charge susceptibility on the resistivity. | 2403.09241v1 |
2024-03-21 | On the lineshapes of temperature-dependent transport measurements of superconductors under pressure | Recent reports of superconductivity in the vicinity of room temperature have
been the subject of discussion by the community. Specifically, features in the
resistance-temperature (R-T) relations have raised questions. We show that many
of these features can arise from previously unaccounted-for dynamic effects
associated with the AC transport techniques often used in high-pressure
experiments. These dynamic AC effects can can cause the apparent resistance
(Rapparent) to diverge from the DC resistance (RDC), sharpen measured
superconducting transitions, and produce other features in the measured R-T
response. We also show that utilizing the full output of phase-sensitive
transport measurements provides a valuable probe of superconducting samples in
difficult to measure systems | 2403.14075v2 |
2024-04-15 | SpamDam: Towards Privacy-Preserving and Adversary-Resistant SMS Spam Detection | In this study, we introduce SpamDam, a SMS spam detection framework designed
to overcome key challenges in detecting and understanding SMS spam, such as the
lack of public SMS spam datasets, increasing privacy concerns of collecting SMS
data, and the need for adversary-resistant detection models. SpamDam comprises
four innovative modules: an SMS spam radar that identifies spam messages from
online social networks(OSNs); an SMS spam inspector for statistical analysis;
SMS spam detectors(SSDs) that enable both central training and federated
learning; and an SSD analyzer that evaluates model resistance against
adversaries in realistic scenarios. Leveraging SpamDam, we have compiled over
76K SMS spam messages from Twitter and Weibo between 2018 and 2023, forming the
largest dataset of its kind. This dataset has enabled new insights into recent
spam campaigns and the training of high-performing binary and multi-label
classifiers for spam detection. Furthermore, effectiveness of federated
learning has been well demonstrated to enable privacy-preserving SMS spam
detection. Additionally, we have rigorously tested the adversarial robustness
of SMS spam detection models, introducing the novel reverse backdoor attack,
which has shown effectiveness and stealthiness in practical tests. | 2404.09481v1 |
2024-04-23 | Sharp ill-posedness for the non-resistive MHD equations in Sobolev spaces | In this paper, we prove a sharp ill-posedness result for the incompressible
non-resistive MHD equations. In any dimension $d\ge 2$, we show the
ill-posedness of the non-resistive MHD equations in
$H^{\frac{d}{2}-1}(\mathbb{R}^d)\times H^{\frac{d}{2}}(\mathbb{R}^d)$, which is
sharp in view of the results of the local well-posedness in
$H^{s-1}(\mathbb{R}^d)\times H^{s}(\mathbb{R}^d)(s>\frac{d}{2})$ established by
Fefferman et al.(Arch. Ration. Mech. Anal., \textbf{223} (2), 677-691, 2017).
Furthermore, we generalize the ill-posedness results from
$H^{\frac{d}{2}-1}(\mathbb{R}^d)\times H^{\frac{d}{2}}(\mathbb{R}^d)$ to Besov
spaces $B^{\frac{d}{p}-1}_{p, q}(\mathbb{R}^d)\times B^{\frac{d}{p}}_{p,
q}(\mathbb{R}^d)$ and $\dot B^{\frac{d}{p}-1}_{p, q}(\mathbb{R}^d)\times \dot
B^{\frac{d}{p}}_{p, q}(\mathbb{R}^d)$ for $1\le p\le\infty, q>1$. Different
from the ill-posedness mechanism of the incompressible Navier-Stokes equations
in $\dot B^{-1}_{\infty, q}$ \cite{B,W}, we construct an initial data such that
the paraproduct terms (low-high frequency interaction) of the nonlinear term
make the main contribution to the norm inflation of the magnetic field. | 2404.14825v1 |
2012-11-05 | Structure and Thermodynamical Properties of Zirconium hydrides from first-principle | Zirconium alloys are used as nuclear fuel cladding material due to their
mechanical and corrosion resistant properties together with their favorable
cross-section for neutron scattering. At running conditions, however, there
will be an increase of hydrogen in the vicinity of the cladding surface at the
water side of the fuel. The hydrogen will diffuse into the cladding material
and at certain conditions, such as lower temperatures and external load,
hydrides will precipitate out in the material and cause well known
embrittlement, blistering and other unwanted effects. Using phase-field methods
it is now possible to model precipitation build-up in metals, for example as a
function of hydrogen concentration, temperature and external load, but the
technique relies on input of parameters, such as the formation energy of the
hydrides and matrix. To that end, we have computed, using the density
functional theory (DFT) code GPAW, the latent heat of fusion as well as solved
the crystal structure for three zirconium hydride polymorphs: \delta-ZrH1.6,
\gamma-ZrH, and \epsilon-ZrH2. | 1211.0858v1 |
2019-05-16 | A multi-physics methodology for four-states of matter | We propose a numerical methodology for the simultaneous numerical simulation
of four states of matter; gas, liquid, elastoplastic solids and plasma. The
distinct, interacting physical processes are described by a combination of
compressible, inert and reactive forms of the Euler equations, multiphase
equations, elastoplastic equations and resistive MHD equations. Combinations of
systems of equations are usually solved by coupling finite element for solid
modelling and CFD models for fluid modelling or including material effects
through boundary conditions rather than full material discretisation. Our
simultaneous solution methodology lies on the recasting of all the equations in
the same, hyperbolic form allowing their solution on the same grid with the
same finite-volume numerical schemes. We use a combination of sharp and diffuse
interface methods to track or capture material interfaces, depending on the
application. The communication between the distinct systems of equations (i.e.,
materials separated by sharp interfaces) is facilitated by means of
mixed-material Riemann solvers at the boundaries of the systems, which
represent physical material boundaries. To this end we derive approximate mixed
Riemann solvers for each pair of the above models based on characteristic
equations. To demonstrate the applicability of the new methodology we consider
a case study where we investigate the possibility of ignition of a combustible
gas that lies over a liquid in a metal container that is struck by a plasma-arc
akin to a lightning strike. We study the effect on the ignition of the metal
container material and conductivity, of the presence of a dielectric coating,
of insensitive combustible gases and sealed and pre-damaged metal surfaces. | 1905.06620v1 |
2017-01-05 | Graphene and its elemental analogue: A molecular dynamics view of fracture phenomenon | Graphene and some graphene like two dimensional materials; hexagonal boron
nitride (hBN) and silicene have unique mechanical properties which severely
limit the suitability of conventional theories used for common brittle and
ductile materials to predict the fracture response of these materials. This
study revealed the fracture response of graphene, hBN and silicene nanosheets
under different tiny crack lengths by molecular dynamics (MD) simulations using
LAMMPS. The useful strength of these large area two dimensional materials are
determined by their fracture toughness. Our study shows a comparative analysis
of mechanical properties among the elemental analogues of graphene and
suggested that hBN can be a good substitute for graphene in terms of mechanical
properties. We have also found that the pre-cracked sheets fail in brittle
manner and their failure is governed by the strength of the atomic bonds at the
crack tip. The MD prediction of fracture toughness shows significant difference
with the fracture toughness determined by Griffth's theory of brittle failure
which restricts the applicability of Griffith's criterion for these materials
in case of nano-cracks. Moreover, the strengths measured in armchair and zigzag
directions of nanosheets of these materials implied that the bonds in armchair
direction has the stronger capability to resist crack propagation compared to
zigzag direction. | 1701.01193v2 |
2022-08-04 | Printing on particles: combining two-photon nanolithography and capillary assembly to fabricate multi-material microstructures | Additive manufacturing at the micro- and nanoscale has seen a recent upsurge
to suit the increasing demand for more elaborate structures. However, the
integration and precise placement of multiple distinct materials at small
scales remain a challenge. To this end, we combine here the directed capillary
assembly of colloidal particles and two-photon direct laser writing (DLW) to
realize a new class of multi-material microstructures. We use DLW both to
fabricate 3D micro-templates to guide the capillary assembly of soft- and hard
colloids, and to link well-defined arrangements of polystyrene or silica
particles produced with capillary assembly, a process we term "printing on
particles". The printing process is based on automated particle recognition
algorithms and enables the user to connect colloids into one- and
two-dimensional tailored structures, including particle clusters and lattices
of varying symmetry and composition, using commercial photo-resists (IP-L or
IP-PDMS). Once printed and developed, the structures can be easily harvested
and re-dispersed in water. The flexibility of our method allows the combination
of a wide range of materials into complex structures, which we envisage will
boost the realization of new systems for a broad range of fields, including
microrobotics, micromanipulation and metamaterials. | 2208.02635v1 |
2023-10-28 | Making the cut: end effects and the benefits of slicing | Cutting mechanics in soft solids have been a subject of study for several
decades, an interest fuelled by the multitude of its applications, including
material testing, manufacturing, and biomedical technology. Wire cutting is the
simplest model system to analyze the cutting resistance of a soft material.
However, even for this simple system, the complex failure mechanisms that
underpin cutting are still not completely understood. Several models that
connect the critical cutting force to the radius of the wire and the key
mechanical properties of the cut material have been proposed. An almost
ubiquitous simplifying assumption is a state of plane (and anti-plane) strain
in the material. In this paper, we show that this assumption can lead to
erroneous conclusions because even such a simple cutting problem is essentially
three-dimensional. A planar approximation restricts the analysis to the stress
distribution in the mid-plane. However, through finite element modeling, we
reveal that the maximal tensile stress - and thus the likely location of cut
initiation - is in fact located in the front plane. Friction reduces the
magnitude of this stress, but this detrimental effect can be counteracted by
large slice-to-push (shear-to-indentation) ratios. The introduction of these
end effects helps reconcile a recent controversy around the role of friction in
wire cutting, for it implies that slicing can indeed reduce required cutting
forces, but only if the slice-push ratio and the friction coefficient are
sufficiently large. Material strain-stiffening reduces the critical indentation
depth required to initiate the cut further and thus needs to be considered when
cutting non-linearly elastic materials. | 2310.18595v1 |
1996-06-27 | Temperature crossovers in cuprates | We study the temperature crossovers seen in the magnetic and transport
properties of cuprates using a nearly antiferromagnetic Fermi liquid model
(NAFLM). For the overdoped cuprates, we find, in agreement with earlier work,
mean-field $z=2$ behavior of the magnetic variables associated with the fact
that the damping rate of their spin fluctuations is essentially independent of
temperature, while the resistivity exhibits a crossover from Fermi liquid
behavior at low temperature to linear-in-T above a certain temperature $T_0$,
due to the proximity of the quasiparticle Fermi surface to the magnetic
Brillouin zone boundary. For the underdoped cuprates we argue that the sequence
of crossovers identified by Barzykin and Pines in the low frequency magnetic
behavior (from mean field $z=2$ at high temperatures, $T>T_{cr}$, to
non-universal $z=1$ scaling behavior at intermediate $T$, $T_*<T<T_{cr}$, to
pseudogap behavior below $T_*$) reflects the development in the electronic
structure of a precursor to a spin-density-wave state. This development begins
at $T_{cr}$ with a thermal evolution of the quasiparticle spectral weight which
brings about temperature dependent spin-damping and ends at $T_*$ where the
Fermi surface has lost pieces near corners of the magnetic Brillouin zone. For
$T_*<T<T_{cr}$ the resistivity is linear in $T$ because this change in spectral
weight does not affect the resistivity significantly; below $T_*$ vertex
corrections act to bring about the measured downturn in $(\rho(T)-\rho(0))/T$
and approximately quadratic in $T$ resistivity for $T\ll T_*$. | 9606208v3 |
2000-05-17 | Coulomb blockade in one-dimensional arrays of high conductance tunnel junctions | Properties of one-dimensional (1D) arrays of low Ohmic tunnel junctions (i.e.
junctions with resistances comparable to, or less than, the quantum resistance
$R_{\rm q}\equiv h/e^2\approx 25.8$ k$\Omega$) have been studied experimentally
and theoretically. Our experimental data demonstrate that -- in agreement with
previous results on single- and double-junction systems -- Coulomb blockade
effects survive even in the strong tunneling regime and are still clearly
visible for junction resistances as low as 1 k$\Omega$. We have developed a
quasiclassical theory of electron transport in junction arrays in the strong
tunneling regime. Good agreement between the predictions of this theory and the
experimental data has been observed. We also show that, due to both heating
effects and a relatively large correction to the linear relation between the
half-width of the conductance dip around zero bias voltage, $V_{1/2}$, and the
measured electronic temperature, such arrays are inferior to those
conventionally used in the Coulomb Blockade Thermometry (CBT). Still, the
desired correction to the half-width, $\Delta V_{1/2}$, can be determined
rather easily and it is proportional to the magnitude of the conductance dip
around zero bias voltage, $\Delta G$. The constant of proportionality is a
function of the ratio of the junction and quantum resistances, $R/R_{\rm q}$,
and it is a pure strong tunneling effect. | 0005283v1 |
2001-09-04 | Magnetotransport of CeRhIn5 | We report measurements of the temperature-dependent anisotropic resistivity
and in-plane magnetoresistance on single crystals of the tetragonal
heavy-fermion antiferromagnet (TN = 3.8 K) CeRhIn5. The measurements are
reported in the temperature range 1.4 K to 300 K and in magnetic fields to 18
tesla. The resistivity is moderately anisotropic, with a room-temperature
c-axis to in-plane resistivity ratio rho_c/rho_a(300 K) = 1.7. rho(T)
measurements on the non-magnetic analog LaRhIn5 indicate that the anisotropy in
the CeRhIn5 resistivity stems predominately from anisotropy in Kondo-derived
magnetic scattering. In the magnetically ordered regime an applied field H
reduces TN only slightly due to the small ordered moment (0.37mu_B) and
magnetic anisotropy. The magnetoresistance (MR) below TN is positive and varies
linearly with H. In the paramagnetic state a positive MR is present below 7.5
K, while a high-field negative contribution is evident at higher temperatures.
The positive contribution decreases in magnitude with increasing temperature.
Above 40 K the positive contribution is no longer observable, and the MR is
negative. The low-T positive MR results from interactions with the
Kondo-coherent state, while the high-T negative MR stems from single-impurity
effects. The H and T-dependent magnetotransport reflects the magnetic
anisotropy and Kondo interactions at play in CeRhIn5. | 0109062v1 |
2002-07-16 | Resistivity, Hall effect and Shubnikov-de Haas oscillations in CeNiSn | The resistivity and Hall effect in CeNiSn are measured at temperatures down
to 35 mK and in magnetic fields up to 20 T with the current applied along the
{\it b} axis. The resistivity at zero field exhibits quadratic temperature
dependence below $\sim$0.16 K with a huge coefficient of the $T^2$ term (54
$\mu$$\Omega$cm/K$^2$). The resistivity as a function of field shows an
anomalous maximum and dip, the positions of which vary with field directions.
Shubnikov-de Haas (SdH) oscillations with a frequency {\it F} of $\sim$100 T
are observed for a wide range of field directions in the {\it ac} and {\it bc}
planes, and the quasiparticle mass is determined to be $\sim$10-20 {\it m}$_e$.
The carrier density is estimated to be $\sim10^{-3}$ electron/Ce. In a narrow
range of field directions in the {\it ac} plane, where the
magnetoresistance-dip anomaly manifests itself clearer than in other field
directions, a higher-frequency ($F=300\sim400\text{T}$) SdH oscillation is
found at high fields above the anomaly. This observation is discussed in terms
of possible field-induced changes in the electronic structure. | 0207379v1 |
2003-03-03 | Systematics in the superconducting and normal state properties in chemically substituted MgB$_{2}$ | The superconducting transition temperature, T$_{C}$, the residual resistivity
$\rho_{0}$ and the slope of resistivity curve at high temperature, d$\rho$/dT,
have been measured in a series of MgB$_{2}$ samples that have been chemically
substituted to varying degree with Li or Cu at the Mg-site and by Li or Cu at
the Mg-site along with C substitution at the B-site. DC resistivity and ac
susceptibility measurements were employed to extract the above parameters.
T$_{C}$ versus the electron count (estimated from simple chemical valence count
arguments) shows a universal behaviour, with T$_{C}$ being constant at the
MgB$_{2}$ value for electron counts lower than in MgB$_{2}$ but rapidly
decreasing for larger electron counts. The temperature dependence of
resistivity in the normal state fits to the Bloch- Gruneisen formula, from
which the Debye temperature, $\theta_{D}$, and the $\rho_{0}$ are extracted.
$\theta_{D}$ variation with T$_{C}$ is not systematic, whereas $\rho_{0}$
versus T$_{C}$ shows a systematic variation that depends on the type of the
chemical substituent. This dependence has a signature of the nature of the
intraband/interband scattering affected by the chemical substitutions.
d$\rho$/dT increases with C substitution, but decreases with Li and Cu
substitution, implying that C substitution leads to the domination of
conductivity by the $\sigma$ band, while in the Li/Cu substituted samples the
$\pi$ band dominates conduction. | 0303022v1 |
2005-05-19 | Non-Gaussian Fluctuations in Biased Resistor Networks: Size Effects versus Universal Behavior | We study the distribution of the resistance fluctuations of biased resistor
networks in nonequilibrium steady states. The stationary conditions arise from
the competition between two stochastic and biased processes of breaking and
recovery of the elementary resistors. The fluctuations of the network
resistance are calculated by Monte Carlo simulations which are performed for
different values of the applied current, for networks of different size and
shape and by considering different levels of intrinsic disorder. The
distribution of the resistance fluctuations generally exhibits relevant
deviations from Gaussianity, in particular when the current approaches the
threshold of electrical breakdown. For two-dimensional systems we have shown
that this non-Gaussianity is in general related to finite size effects, thus it
vanishes in the thermodynamic limit, with the remarkable exception of highly
disordered networks. For these systems, close to the critical point of the
conductor-insulator transition, non-Gaussianity persists in the large size
limit and it is well described by the universal Bramwell-Holdsworth-Pinton
distribution. In particular, here we analyze the role of the shape of the
network on the distribution of the resistance fluctuations. Precisely, we
consider quasi-one-dimensional networks elongated along the direction of the
applied current or trasversal to it. A significant anisotropy is found for the
properties of the distribution. These results apply to conducting thin films or
wires with granular structure stressed by high current densities. | 0505478v1 |
2007-01-05 | Colossal electroresistance in ferromagnetic insulating state of single crystal Nd$_0.7$Pb$_0.3$MnO$_3$ | Colossal electroresistance (CER) has been observed in the ferromagnetic
insulating (FMI) state of a manganite. Notably, the CER in the FMI state occurs
in the absence of magnetoresistance (MR). Measurements of electroresistance
(ER) and current induced resistivity switching have been performed in the
ferromagnetic insulating state of a single crystal manganite of composition
Nd$_0.7$Pb$_0.3$MnO$_3$ (NPMO30). The sample has a paramagnetic to
ferromagnetic (Curie) transition temperature, Tc = 150 K and the ferromagnetic
insulating state is realized for temperatures, T <~ 130 K. The colossal
electroresistance, arising from a strongly nonlinear dependence of resistivity
($\rho$) on current density (j), attains a large value ($\approx 100%$) in the
ferromagnetic insulating state. The severity of this nonlinear behavior of
resistivity at high current densities is progressively enhanced with decreasing
temperature, resulting ultimately, in a regime of negative differential
resistivity (NDR, d$\rho$/dj < 0) for temperatures <~ 25 K. Concomitant with
the build-up of the ER however, is a collapse of the MR to a small value (<
20%) even in magnetic field, H = 7 T. This demonstrates that the mechanisms
that give rise to ER and MR are effectively decoupled in the ferromagnetic
insulating phase of manganites. We establish that, the behavior of
ferromagnetic insulating phase is distinct from the ferromagnetic metallic
(FMM) phase as well as the charge ordered insulating (COI) phase, which are the
two commonly realized ground state phases of manganites. | 0701090v1 |
2005-09-05 | Distribution of Return Periods of Rare Events in Correlated Time Series | We study the effect on the distribution of return periods of rare events of
the presence in a time series of finite-term correlations with non-exponential
decay. Precisely, we analyze the auto-correlation function and the statistics
of the return intervals of extreme values of the resistance fluctuations
displayed by a resistor with granular structure in a nonequilibrium stationary
state. The resistance fluctuations, $\delta R$, are calculated by Monte Carlo
simulations using the SBRN model introduced some years ago by Pennetta,
Tref\'an and Reggiani and based on a resistor network approach. A rare event
occurs when $\delta R$ overcomes a threshold value $q$ significantly higher
than the average value of the resistance. We have found that for highly
disordered networks, when the auto-correlation function displays a
non-exponential decay but yet the resistance fluctuations are characterized by
a finite correlation time, the distribution of return intervals of the extreme
values is well described by a stretched exponential, with exponent largely
independent of the threshold $q$. We discuss this result and some of the main
open questions related to it, also in connection with very recent findings by
other authors concerning the observation of stretched exponential distributions
of return intervals of extreme events in long-term correlated time series. | 0509037v2 |
2007-11-08 | Study of Intrinsic Spin Hall Effect and Orbital Hall Effect in 4d- and 5d- Transition Metals | We study the intrinsic spin Hall conductivity (SHC) in various
$5d$-transition metals (Ta, W, Re, Os, Ir, Pt, and Au) and 4d-transition metals
(Nb, Mo, Tc, Ru, Rh, Pd, and Ag) based on the Naval Research Laboratory
tight-binding model, which enables us to perform quantitatively reliable
analysis. In each metal, the obtained intrinsic SHC is independent of
resistivity in the low resistive regime ($\rho < 50 \mu\Omega\text{cm}$)
whereas it decreases in proportion to $\rho^{-2}$ in the high resistive regime.
In the low resistive regime, the SHC takes a large positive value in Pt and Pd,
both of which have approximately nine $d$-electrons per ion ($n_d=9$). On the
other hand, the SHC takes a large negative value in Ta, Nb, W, and Mo where
$n_d<5$. In transition metals, a conduction electron acquires the
trajectory-dependent phase factor that originates from the atomic wavefunction.
This phase factor, which is reminiscent of the Aharonov-Bohm phase, is the
origin of the SHC in paramagnetic metals and that of the anomalous Hall
conductivity in ferromagnetic metals. Furthermore, each transition metal shows
huge and positive $d$-orbital Hall conductivity (OHC), independently of the
strength of the spin-orbit interaction (SOI). Since the OHC is much larger than
the SHC, it will be possible to realize a {\it orbitronics device} made of
transition metals. | 0711.1263v4 |
2008-03-06 | Zinc adaptation and resistance to cadmium toxicity in mammalian cells. Molecular insight by proteomic analysis | To identify proteins involved in cellular adaptive responses to zinc, a
comparative proteome analysis between a previously developed high zinc- and
cadmium- resistant human epithelial cell line (HZR) and the parental HeLa cells
has been carried out. Differentially produced proteins included co-chaperones,
proteins associated with oxido-reductase activities, and ubiquitin. Biochemical
pathways to which these proteins belong were probed for their involvement in
the resistance of both cell lines against cadmium toxicity. Among endoplasmic
reticulum stressors, thapsigargin sensitized HZR cells, but not HeLa cells, to
cadmium toxicity more acutely than tunicamycin, implying that these cells
heavily relied on proper intracellular calcium distribution. The similar
sensitivity of both HeLa and HZR cells to inhibitors of the proteasome, such as
MG-132 or lactacystin, excluded improved proteasome activity as a mechanism
associated with zinc adaptation of HZR cells. The enzyme
4-hydroxyphenylpyruvate dioxygenase was overproduced in HZR cells as compared
to HeLa cells. It transforms 4-hydroxyphenylpyruvate to homogentisate in the
second step of tyrosine catabolism. Inhibition of 4-hydroxyphenylpyruvate
dioxygenase decreased the resistance of HZR cells against cadmium, but not that
of HeLa cells, suggesting that adaptation to zinc overload and increased
4-hydroxyphenylpyruvate removal are linked in HZR cells | 0803.0850v1 |
2008-03-24 | Effect of static and dynamic disorder on electronic transport of $RCo_2$ compounds: a study of $Ho(Al_xCo_{1-x})_2$ alloys | We present experimental results on thermoelectric power ({\em S}) and
electrical resistivity ($\rho $) of pseudobinary alloys
Ho(Al$_x$Co$_{1-x}$)$_2$ ($0 \leq x \leq 0.1 $), in the temperature range 4.2 K
to 300 K. The work focuses on the effects of static (induced by alloying) and
dynamic (induced by temperature) disorder on the magnetic state and electronic
transport in a metallic system with itinerant metamagnetic instability. Spatial
fluctuations of the local magnetic susceptibility in the alloys lead to a
development of a partially ordered magnetic ground state of the itinerant 3d
electron system. This results in a strong increase of the residual resistivity
and a suppression of the temperature-dependent resistivity. Thermopower
exhibits a complex temperature variation in both the magnetically ordered and
in the paramagnetic state. This complex temperature variation is referred to
the electronic density of states features in vicinity of Fermi energy and to
the interplay of magnetic and impurity scattering. Our results indicate that
the magnetic enhancement of the Co 3d-band in RCo$_{\rm 2}$--based alloys upon
a substitution of Co by non-magnetic elements is mainly related to a
progressive localization of the Co -- 3d electrons caused by disorder. We show
that the magnitude of the resistivity jump at the Curie temperature for
RCo$_{\rm 2}$ compounds exhibiting a first order phase transition is a
non-monotonic function of the Curie temperature due to a saturation of the
3d--band spin fluctuation magnitude at high temperatures. | 0803.3380v3 |
2011-05-17 | Linear-T scattering and pairing from antiferromagnetic fluctuations in the (TMTSF)_2X organic superconductors | An exhaustive investigation of metallic electronic transport and
superconductivity of organic superconductors (TMTSF)_2PF_6 and (TMTSF)_2ClO_4
in the Pressure-Temperature phase diagram between T=0 and 20 K and a
theoretical description based on the weak coupling renormalization group method
are reported. The analysis of the data reveals a high temperature domain
(T\approx 20 K) in which a regular T^2 electron-electron Umklapp scattering
obeys a Kadowaki-Woods law and a low temperature regime (T< 8 K) where the
resistivity is dominated by a linear-in temperature component. In both
compounds a correlated behavior exists between the linear transport and the
extra nuclear spin-lattice relaxation due to antiferromagnetic fluctuations. In
addition, a tight connection is clearly established between linear transport
and T_c. We propose a theoretical description of the anomalous resistivity
based on a weak coupling renormalization group determination of
electron-electron scattering rate. A linear resistivity is found and its origin
lies in antiferromagnetic correlations sustained by Cooper pairing via
constructive interference. The decay of the linear resistivity term under
pressure is correlated with the strength of antiferromagnetic spin correlations
and T_c, along with an unusual build-up of the Fermi liquid scattering. The
results capture the key features of the low temperature electrical transport in
the Bechgaard salts. | 1105.3322v2 |
2011-09-18 | Vortex glass line and vortex liquid resistivity in doped BaFe2As2 single crystals | The vortex liquid-to-glass transition has been studied in Ba0.72K0.28Fe2As2,
Ba0.9Co0.1Fe2As2, and Ba(Fe0.45Ni0.05)2As2 single crystal with superconducting
transition temperature, Tc = 31.7, 17.3, and 18 K, respectively, by
magnetoresistance measurements. For temperatures below Tc, the resistivity
curves were measured in magnetic fields within the range of 0 \leq B \leq 13 T,
and the pinning potential was scaled according to a modified model for vortex
liquid resistivity. Good scaling of the resistivity {\rho}(B, T) and the
effective pinning energy U0(B,T) was obtained with the critical exponents s and
B0. The vortex state is three-dimensional at temperatures lower than a
characteristic temperature T*. The vortex phase diagram was determined based on
the evolution of the vortex-glass transition temperature Tg with magnetic field
and the upper critical field, Hc2. We found that non-magnetic K doping results
in a high glass line close to the Hc2, while magnetic Ni and Co doping cause a
low glass line which is far away from the Hc2. Our results suggest that
non-magnetic induced disorder is more favourable for enhancement of pinning
strength compared to magnetic induced disorder. Our results show that the
pinning potential is responsible for the difference in the glass states. | 1109.3837v1 |
2011-10-24 | Manifestations of multiple-carrier charge transport in the magnetostructurally ordered phase of undoped BaFe$_2$As$_2$ | We investigated the transport properties of BaFe$_2$As$_2$ single crystals
before and after annealing with BaAs powder. The annealing remarkably improves
transport properties, in particular the magnitude of residual resistivity which
decreases by a factor of more than 10. From the resistivity measurement on
detwinned crystals we found that the anisotropy of the in-plane resistivity is
remarkably diminished after annealing, indicative of dominant contributions to
the charge transport from the carriers with isotropic and high mobility below
magnetostructural transition temperature $T_{\rm s}$ and the absence of nematic
state above $T_{\rm s}$. We found that the Hall resistivity shows strong
non-linearity against magnetic field and the magnetoresistance becomes very
large at low temperatures. These results give evidence for the manifestation of
multiple carriers with distinct characters in the ordered phase below $T_{\rm
s}$. By analyzing the magnetic field dependences, we found that at least three
carriers equally contribute to the charge transport in the ordered phase, which
is in good agreement with the results of recent quantum oscillation
measurements. | 1110.5125v3 |
2012-02-14 | Influence of e-e scattering on the temperature dependence of the resistance of a classical ballistic point contact in a two-dimensional electron system | We experimentally investigate the temperature (T) dependence of the
resistance of a classical ballistic point contact (PC) in a two-dimensional
electron system (2DES). The split-gate PC is realized in a high-quality
AlGaAs/GaAs heterostructure. The PC resistance is found to drop by more than
10% as T is raised from 0.5 K to 4.2 K. In the absence of a magnetic field, the
T dependence is roughly linear below 2 K and tends to saturate at higher T.
Perpendicular magnetic fields on the order of a few 10 mT suppress the
T-dependent contribution dR. This effect is more pronounced at lower
temperatures, causing a crossover to a nearly parabolic T dependence in a
magnetic field. The normalized magnetic field dependencies dR(B) permit an
empiric single parameter scaling in a wide range of PC gate voltages. These
observations give strong evidence for the influence of electron-electron (e-e)
scattering on the resistance of ballistic PCs. Our results are in qualitative
agreement with a recent theory of the e-e scattering based T dependence of the
conductance of classical ballistic PCs [ Phys. Rev. Lett. 101 216807 (2008) and
Phys. Rev. B 81 125316 (2010)]. | 1202.2952v3 |
2012-07-06 | Universal sheet resistance and revised phase diagram of the cuprate high-temperature superconductors | Upon introducing charge carriers into the copper-oxygen sheets of the
enigmatic lamellar cuprates the ground state evolves from an insulator into a
superconductor, and eventually into a seemingly conventional metal (a Fermi
liquid). Much has remained elusive about the nature of this evolution and about
the peculiar metallic state at intermediate hole-carrier concentrations (p).
The planar resistivity of this unconventional metal exhibits a linear
temperature dependence (\rho $\propto$ T) that is disrupted upon cooling toward
the superconducting state by the opening of a partial gap (the pseudogap) on
the Fermi surface. Here we first demonstrate for the quintessential compound
HgBa$_2$CuO$_{4+\delta}$ a dramatic switch from linear to purely quadratic
(Fermi-liquid-like, \rho $\propto$ T$^2$) resistive behavior in the pseudogap
regime. Despite the considerable variation in crystal structures and disorder
among different compounds, our result together with prior work gives new
insight into the p-T phase diagram and reveals the fundamental resistance per
copper-oxygen sheet in both linear (\rho_S = A_{1S} T) and quadratic (\rho_S =
A_{2S} T$^2$) regimes, with A_{1S} $\propto$ A_{2S} $\propto$ 1/p. Theoretical
models can now be benchmarked against this remarkably simple universal
behavior. Deviations from this underlying behavior can be expected to lead to
new insights into the non-universal features exhibited by certain compounds. | 1207.1504v2 |
2013-05-14 | Differences in the effects of turns and constrictions on the resistive response in current-biased superconducting wire after single photon absorption | We study how turns and constrictions affect the resistive response of the
superconducting wire after instant in time and local in space heating, which
models the absorption of the single photon by the wire. We find that the
presence of constriction favors detection of photons of various energies but
the presence of turn increases only ability to detect relatively "low" energy
photons. The main reason is that in case of constriction the current density is
increased over whole length and width of the constriction while in case of the
turn the current density is enhanced only near the inner corner of the turn. It
results in inhomogeneous Joule heating near the turn and worsens the conditions
for appearance of the normal domain at relatively small currents when the
"high" energy photons already could create normal domain in straight part of
the wire. We also find that the amplitude of the voltage pulse depends on the
place where the photon is absorbed. It is the smallest one when photon is
absorbed near the turn and it is the largest one when photon is absorbed near
the constriction. This effect comes from the difference in resistance of
constriction and the turn in the normal state from the resistance of the rest
of the wire. | 1305.3110v1 |
2013-05-31 | Numerical Treatment of Anisotropic Radiation Field Coupling with the Relativistic Resistive Magnetofluids | We develop a numerical scheme for solving a fully special relativistic
resistive radiation magnetohydrodynamics. Our code guarantees conservations of
total mass, momentum and energy. Radiation energy density and radiation flux
are consistently updated using the M-1 closure method, which can resolve an
anisotropic radiation fields in contrast to the Eddington approximation as well
as the flux-limited diffusion approximation. For the resistive part, we adopt a
simple form of the Ohm's law. The advection terms are explicitly solved with an
approximate Riemann solver, mainly HLL scheme, and HLLC and HLLD schemes for
some tests. The source terms, which describe the gas-radiation interaction and
the magnetic energy dissipation, are implicitly integrated, relaxing the
Courant-Friedrichs-Lewy condition even in optically thick regime or a large
magnetic Reynolds number regime. Although we need to invert $4\times 4$ (for
gas-radiation interaction) and $3\times 3$ (for magnetic energy dissipation)
matrices at each grid point for implicit integration, they are obtained
analytically without preventing massive parallel computing. We show that our
code gives reasonable outcomes in numerical tests for ideal
magnetohydrodynamics, propagating radiation, and radiation hydrodynamics. We
also applied our resistive code to the relativistic Petschek type magnetic
reconnection, revealing the reduction of the reconnection rate via the
radiation drag. | 1306.0049v1 |
2014-02-06 | Scattering mechanisms in textured FeGe thin films: magnetoresistance and the anomalous Hall effect | A textured thin film of FeGe was grown by magnetron sputtering with a
helimagnetic ordering temperature of TN = 276 +/- 2 K. From 5 K to room
temperature a variety of scattering processes contribute towards the overall
longitudinal and Hall resistivities. These were studied by combining
magnetometry and magnetotransport measurements. The high-field
magnetoresistance (MR) displays three clear temperature regimes: Lorentz force
MR dominates at low temperatures, above T ~ 80 K scattering from spin-waves
predominates, whilst finally for T > 200 K scattering from fluctuating local
moments describes the MR. At low fields, where the magnetisation is no longer
technically saturated, we find a scaling of magnetoresistance with the square
of the magnetisation, indicating that the MR due to the unwinding of spins in
the conical phase arises from a similar mechanism to that in magnetic domain
walls. This MR is only visible up to a temperature of about 200 K. No features
can be found in the temperature or field dependence of the longitudinal
resistivity that belie the presence of the underlying magnetic phase transition
at TN: the marked changes in behavior are at much lower temperatures. The
anomalous Hall effect has a dramatic temperature dependence in which the
anomalous Hall resistivity scales quadratically with the longitudinal
resistivity: comparison with anomalous Hall scaling theory shows that our
system is in the intrinsic 'moderately dirty' regime. Lastly, we find evidence
of a topological Hall effect of size 100 ~Ohm cm. | 1402.1276v2 |
2014-05-16 | Extracting superconducting parameters from surface resistivity by using inside temperatures of SRF cavities | The surface resistance of an RF superconductor depends on the surface
temperature, the residual resistance and various superconductor parameters,
e.g. the energy gap, and the electron mean free path. These parameters can be
determined by measuring the quality factor Q0 of a SRF cavity in helium-baths
of different temperatures. The surface resistance can be computed from Q0 for
any cavity geometry, but it is not trivial to determine the temperature of the
surface when only the temperature of the helium bath is known.
Traditionally, it was approximated that the surface temperature on the inner
surface of the cavity was the same as the temperature of the helium bath. This
is a good approximation at small RF-fields on the surface, but to determine the
field dependence of Rs, one cannot be restricted to small field losses.
Here we show the following: (1) How computer simulations can be used to
determine the inside temperature Tin so that Rs(Tin) can then be used to
extract the superconducting parameters. The computer code combines the
well-known programs, the HEAT code and the SRIMP code. (2) How large an error
is created when assuming the surface temperature is same as the temperature of
the helium bath? It turns out that this error is at least 10% at high RF-fields
in typical cases. | 1405.4226v1 |
2014-05-23 | Evolution of Anisotropic In-plane Resistivity with doping level in Ca$_{1-x}$Na$_x$Fe$_2$As$_2$ Single Crystals | We measured the in-plane resistivity anisotropy in the underdoped
Ca$_{1-x}$Na$_x$Fe$_2$As$_2$ single crystals. The anisotropy (indicated by
$\rho_{\rm b} - \rho_{\rm a}$) appears below a temperature well above magnetic
transition temperature $T_{\rm N}$, being positive ($\rho_{\rm b} - \rho_{\rm
a} > 0$) as $x\leq$ 0.14. With increasing the doping level to $x$ = 0.19, an
intersection between $\rho_{\rm b}$ and $\rho_{\rm a}$ is observed upon
cooling, with $\rho_{\rm b} - \rho_{\rm a} < 0$ at low-temperature deep inside
a magnetically ordered state, while $\rho_{\rm b} - \rho_{\rm a}> 0$ at high
temperature. Subsequently, further increase of hole concentration leads to a
negative anisotropy $\rho_{\rm b} - \rho_{\rm a} < 0$ in the whole temperature
range. These results manifest that the anisotropic behavior of resistivity in
the magnetically ordered state depends strongly on the competition of the
contributions from different mechanisms, and the competition between the two
contributions results in a complicated evolution of the anisotropy of in-plane
resistivity with doping level. | 1405.6199v1 |
2014-10-08 | A Complementary Resistive Switch-based Crossbar Array Adder | Redox-based resistive switching devices (ReRAM) are an emerging class of
non-volatile storage elements suited for nanoscale memory applications. In
terms of logic operations, ReRAM devices were suggested to be used as
programmable interconnects, large-scale look-up tables or for sequential logic
operations. However, without additional selector devices these approaches are
not suited for use in large scale nanocrossbar memory arrays, which is the
preferred architecture for ReRAM devices due to the minimum area consumption.
To overcome this issue for the sequential logic approach, we recently
introduced a novel concept, which is suited for passive crossbar arrays using
complementary resistive switches (CRSs). CRS cells offer two high resistive
storage states, and thus, parasitic sneak currents are efficiently avoided.
However, until now the CRS-based logic-in-memory approach was only shown to be
able to perform basic Boolean logic operations using a single CRS cell. In this
paper, we introduce two multi-bit adder schemes using the CRS-based
logic-in-memory approach. We proof the concepts by means of SPICE simulations
using a dynamical memristive device model of a ReRAM cell. Finally, we show the
advantages of our novel adder concept in terms of step count and number of
devices in comparison to a recently published adder approach, which applies the
conventional ReRAM-based sequential logic concept introduced by Borghetti et
al. | 1410.2031v2 |
2014-10-13 | Resistant Multiple Sparse Canonical Correlation | Canonical Correlation Analysis (CCA) is a multivariate technique that takes
two datasets and forms the most highly correlated possible pairs of linear
combinations between them. Each subsequent pair of linear combinations is
orthogonal to the preceding pair, meaning that new information is gleaned from
each pair. By looking at the magnitude of coefficient values, we can find out
which variables can be grouped together, thus better understanding multiple
interactions that are otherwise difficult to compute or grasp intuitively.
CCA appears to have quite powerful applications to high throughput data, as
we can use it to discover, for example, relationships between gene expression
and gene copy number variation. One of the biggest problems of CCA is that the
number of variables (often upwards of 10,000) makes biological interpretation
of linear combinations nearly impossible. To limit variable output, we have
employed a method known as Sparse Canonical Correlation Analysis (SCCA), while
adding estimation which is resistant to extreme observations or other types of
deviant data. In this paper, we have demonstrated the success of resistant
estimation in variable selection using SCCA. Additionally, we have used SCCA to
find multiple canonical pairs for extended knowledge about the datasets at
hand. Again, using resistant estimators provided more accurate estimates than
standard estimators in the multiple canonical correlation setting.
R code is available and documented at https://github.com/hardin47/rmscca. | 1410.3355v2 |
2014-12-19 | Magnetoresistance near a quantum critical point | In metals near a quantum critical point, the electrical resistance is thought
to be determined by the lifetime of the carriers of current, rather than the
scattering from defects. The observation of $T$-linear resistivity suggests
that the lifetime only depends on temperature, implying the vanishing of an
intrinsic energy scale and the presence of a quantum critical point. Our data
suggest that this concept extends to the magnetic field dependence of the
resistivity in the unconventional superconductor
BaFe$_2$(As$_{1-x}$P$_{x}$)$_2$ near its quantum critical point. We find that
the lifetime depends on magnetic field in the same way as it depends on
temperature, scaled by the ratio of two fundamental constants $\mu_B/k_B$.
These measurements imply that high magnetic fields probe the same quantum
dynamics that give rise to the $T$-linear resistivity, revealing a novel kind
of magnetoresistance that does not depend on details of the Fermi surface, but
rather on the balance of thermal and magnetic energy scales. This opens new
opportunities for the investigation of transport near a quantum critical point
by using magnetic fields to couple selectively to charge, spin and spatial
anisotropies. | 1412.6484v2 |
2015-08-14 | Lattice Boltzmann model for resistive relativistic magnetohydrodynamics | In this paper, we develop a lattice Boltzmann model for relativistic
magnetohydrodynamics (MHD). Even though the model is derived for resistive MHD,
it is shown that it is numerically robust even in the high conductivity (ideal
MHD) limit. In order to validate the numerical method, test simulations are
carried out for both ideal and resistive limits, namely the propagation of
Alfv\'en waves in the ideal MHD and the evolution of current sheets in the
resistive regime, where very good agreement is observed comparing to the
analytical results. Additionally, two-dimensional magnetic reconnection driven
by Kelvin-Helmholtz instability is studied and the effects of different
parameters on the reconnection rate are investigated. It is shown that the
density ratio has negligible effect on the magnetic reconnection rate, while an
increase in shear velocity decreases the reconnection rate. Additionally, it is
found that the reconnection rate is proportional to $\sigma^{-\frac{1}{2}}$,
$\sigma$ being the conductivity, which is in agreement with the scaling law of
the Sweet-Parker model. Finally, the numerical model is used to study the
magnetic reconnection in a stellar flare. Three-dimensional simulation suggests
that the reconnection between the background and flux rope magnetic lines in a
stellar flare can take place as a result of a shear velocity in the
photosphere. | 1508.03452v1 |
2015-10-12 | First in-beam studies of a Resistive-Plate WELL gaseous multiplier | We present the results of the first in-beam studies of a medium size
(10$\times$10 cm$^2$) Resistive-Plate WELL (RPWELL): a single-sided THGEM
coupled to a pad anode through a resistive layer of high bulk resistivity
($\sim$10$^9 \Omega$cm). The 6.2~mm thick (excluding readout electronics)
single-stage detector was studied with 150~GeV muons and pions. Signals were
recorded from 1$\times$1 cm$^2$ square copper pads with APV25-SRS readout
electronics. The single-element detector was operated in Ne\(5%
$\mathrm{CH_{4}}$) at a gas gain of a few times 10$^4$, reaching 99$\%$
detection efficiency at average pad multiplicity of $\sim$1.2. Operation at
particle fluxes up to $\sim$10$^4$ Hz/cm$^2$ resulted in $\sim$23$\%$ gain drop
leading to $\sim$5$\%$ efficiency loss. The striking feature was the
discharge-free operation, also in intense pion beams. These results pave the
way towards robust, efficient large-scale detectors for applications requiring
economic solutions at moderate spatial and energy resolutions. | 1510.03116v2 |
2016-04-14 | Magnetotransport of single crystalline YSb | We report magnetic field dependent transport measurements on a single crystal
of cubic YSb together with first principles calculations of its electronic
structure. The transverse magnetoresistance does not saturate up to 9 T and
attains a value of 75,000 % at 1.8 K. The Hall coefficient is electron-like at
high temperature, changes sign to hole-like between 110 and 50 K, and again
becomes electron-like below 50 K. First principles calculations show that YSb
is a compensated semimetal with a qualitatively similar electronic structure to
that of isostructural LaSb and LaBi, but with larger Fermi surface volume. The
measured electron carrier density and Hall mobility calculated at 1.8 K, based
on a single band approximation, are 6.5$\times10^{20}/$cm$^{3}$ and
6.2$\times10^{4}$cm$^{2}$/Vs, respectively. These values are comparable with
those reported for LaBi and LaSb. Like LaBi and LaSb, YSb undergoes a magnetic
field-induced metal-insulator-like transition below a characteristic
temperature T$_{m}$, with resistivity saturation below 13 K. Thickness
dependent electrical resistance measurements show a deviation of the resistance
behavior from that expected for a normal metal; however, they do not
unambiguously establish surface conduction as the mechanism for the resistivity
plateau. | 1604.04232v1 |
2017-02-14 | A magnetic skyrmion as a non-linear resistive element - a potential building block for reservoir computing | Inspired by the human brain, there is a strong effort to find alternative
models of information processing capable of imitating the high energy
efficiency of neuromorphic information processing. One possible realization of
cognitive computing are reservoir computing networks. These networks are built
out of non-linear resistive elements which are recursively connected. We
propose that a skyrmion network embedded in frustrated magnetic films may
provide a suitable physical implementation for reservoir computing
applications. The significant key ingredient of such a network is a
two-terminal device with non-linear voltage characteristics originating from
single-layer magnetoresistive effects, like the anisotropic magnetoresistance
or the recently discovered non-collinear magnetoresistance. The most basic
element for a reservoir computing network built from "skyrmion fabrics" is a
single skyrmion embedded in a ferromagnetic ribbon. In order to pave the way
towards reservoir computing systems based on skyrmion fabrics, here we simulate
and analyze i) the current flow through a single magnetic skyrmion due to the
anisotropic magneto-resistive effect and ii) the combined physics of local
pinning and the anisotropic magneto-resistive effect. | 1702.04298v2 |
2017-06-15 | MAGNUS: A new resistive MHD code with heat flow terms | We present a new magnetohydrodynamic (MHD) code for the simulation of wave
propagation in the solar atmosphere, under the effects of electrical
resistivity, but not dominant, and heat transference in a uniform 3D grid. The
code is based on the finite volume method combined with the HLLE and HLLC
approximate Riemann solvers, which use different slope limiters like MINMOD,
MC, and WENO5. In order to control the growth of the divergence of the magnetic
field, due to numerical errors, we apply the Flux Constrained Transport method,
which is described in detail to understand how the resistive terms are included
in the algorithm. In our results, it is verified that this method preserves the
divergence of the magnetic fields within the machine round-off error. For the
validation of the accuracy and efficiency of the schemes implemented in the
code, we present some numerical tests in 1D and 2D for the ideal MHD. Later, we
show one test for the resistivity in a magnetic reconnection process and one
for the thermal conduction, where the temperature is advected by the magnetic
field lines. Moreover, we display two numerical problems associated with the
MHD wave propagation. The first one corresponds to a 3D evolution of a vertical
velocity pulse at the photosphere-transition-corona region, while the second
one consists in a 2D simulation of a transverse velocity pulse in a coronal
loop. | 1706.05110v1 |
2018-02-06 | Radiation resistant LGAD design | In this paper, we report on the radiation resistance of 50-micron thick LGAD
detectors manufactured at the Fondazione Bruno Kessler employing several
different doping combinations of the gain layer. LGAD detectors with gain layer
doping of Boron, Boron low-diffusion, Gallium, Carbonated Boron and Carbonated
Gallium have been designed and successfully produced. These sensors have been
exposed to neutron fluences up to $\phi_n \sim 3 \cdot 10^{16}\; n/cm^2$ and to
proton fluences up to $\phi_p \sim 9\cdot10^{15}\; p/cm^2$ to test their
radiation resistance. The experimental results show that Gallium-doped LGADs
are more heavily affected by initial acceptor removal than Boron-doped LGAD,
while the presence of Carbon reduces initial acceptor removal both for Gallium
and Boron doping. Boron low-diffusion shows a higher radiation resistance than
that of standard Boron implant, indicating a dependence of the initial acceptor
removal mechanism upon the implant width. This study also demonstrates that
proton irradiation is at least twice more effective in producing initial
acceptor removal, making proton irradiation far more damaging than neutron
irradiation. | 1802.01745v4 |
2018-04-14 | Non-resistive dissipative magnetohydrodynamics from the Boltzmann equation in the 14-moment approximation | We derive the equations of motion of relativistic, non-resistive,
second-order dissipative magnetohydrodynamics from the Boltzmann equation using
the method of moments. We assume the fluid to be composed of a single type of
point-like particles with vanishing dipole moment or spin, so that the fluid
has vanishing magnetization and polarization. In a first approximation, we
assume the fluid to be non-resistive, which allows to express the electric
field in terms of the magnetic field. We derive equations of motion for the
irreducible moments of the deviation of the single-particle distribution
function from local thermodynamical equilibrium. We analyze the Navier-Stokes
limit of these equations, reproducing previous results for the structure of the
first-order transport coefficients. Finally, we truncate the system of
equations for the irreducible moments using the 14-moment approximation,
deriving the equations of motion of relativistic, non-resistive, second-order
dissipative magnetohydrodynamics. We also give expressions for the new
transport coefficients appearing due to the coupling of the magnetic field to
the dissipative quantities. | 1804.05210v2 |
2018-03-30 | Linearity Analysis of the Common Collector Amplifier, or Emitter Follower | A recently introduced Early modeling of transistors is applied to the study
of the common collector amplifier (or emitter follower), an important type of
electronic circuit typically employed as buffer, being characterized by near
unit voltage gain, high input resistance, and low output resistance. The Early
equivalent model is applied to derive a simple representation that is simple
and yet capable of incorporating the transistor non-linearities implied by the
Early effect. Mathematical expressions are obtained describing completely the
circuit operation in terms of currents and voltages, allowing accurate
estimation of the average voltage gain, total harmonic distortion (THD), and
average input and output resistances. Prototypes of small signal silicon
transistors of types NPN and PNP obtained in a previous work are used to
discuss the respectively implied properties of the common collector transistor.
In addition to confirming the importance of the trade-off of current gain for
the desired properties, it is also shown that sub-optimal performance can be
obtained in case the base and emitter resistances are not properly chosen. Even
so, the limited current gain implied by real-world NPN and PNP small signal
silicon devices implies some performance constraints. In particular, it has
been observed that the THD tends to be larger for PNP devices than NPN
counterparts with the same average current gain. The obtained results pave the
way not only to complementary analytical studies, but also provide guidance for
design and implementation of improved common collector configurations. | 1805.02705v1 |
2018-11-23 | Oxygen vacancies dynamics in redox-based interfaces: Tailoring the memristive response | Redox-based memristive devices are among the alternatives for the next
generation of non volatile memories, but also candidates to emulate the
behavior of synapses in neuromorphic computing devices. It is nowadays well
established that the motion of oxygen vacancies (OV) at the nanoscale is the
key mechanism to reversibly switch metal/insulator/metal structures from
insulating to conducting, i.e. to accomplish the resistive switching effect.
The control of OV dynamics has a direct effect on the resistance changes, and
therefore on different figures of memristive devices, such as switching speed,
retention, endurance or energy consumption. Advances in this direction demand
not only experimental techniques that allow for measurements of OV dynamics,
but also of theoretical studies that shed light on the involved mechanisms.
Along this goal, we analize the OV dynamics in redox interfaces formed when an
oxidizable metallic electrode is in contact with the insulating oxide. We show
how the transfer of OV can be manipulated by using different electrical stimuli
protocols to optimize device figures such as the ON/OFF ratio or the energy
dissipation linked to the writing process. Analytical expressions for attained
resistance values, including the high and low resistance states are derived in
terms of total transferred OV in a nanoscale region of the interface. Our
predictions are validated with experiments performed in
Ti/La$_{1/3}$Ca$_{2/3}$MnO$_{3}$ redox memristive devices. | 1811.09528v1 |
2014-08-14 | Crystal growth and annealing study of fragile, non-bulk superconductivity in YFe$_2$Ge$_2$ | We investigated the occurrence and nature of superconductivity in single
crystals of YFe$_2$Ge$_2$ grown out of Sn flux by employing x-ray diffraction,
electrical resistivity, and specific heat measurements. We found that the
residual resistivity ratio (RRR) of single crystals can be greatly improved,
reaching as high as $\sim$60, by decanting the crystals from the molten Sn at
$\sim$350$^\circ$C and/or by annealing at temperatures between 550$^\circ$C and
600$^\circ$C. We found that samples with RRR $\gtrsim$ 34 showed resistive
signatures of superconductivity with the onset of the superconducting
transition $T_c\approx1.4$ K. RRR values vary between 35 and 65 with, on
average, no systematic change in $T_c$ value, indicating that systematic
changes in RRR do not lead to comparable changes in $T_c$. Specific heat
measurements on samples that showed clear resistive signatures of a
superconducting transition did not show any signature of a superconducting
phase transition, which suggests that the superconductivity observed in this
compound is either some sort of filamentary, strain stabilized
superconductivity associated with small amounts of stressed YFe$_2$Ge$_2$
(perhaps at twin boundaries or dislocations) or is a second crystallographic
phase present at levels below detection capability of conventional powder x-ray
techniques. | 1408.3319v1 |
2019-07-17 | A Nanomagnetic Voltage-Tunable Correlation Generator between Two Random Bit Streams for Stochastic Computing | Graphical probabilistic circuit models of stochastic computing are more
powerful than the predominant deep learning models, but also have more
demanding requirements. For example, they require "programmable stochasticity",
e.g. generating two random binary bit streams with tunable amount of
correlation between the corresponding bits in the two streams. Electronic
implementation of such a system would call for several components leaving a
large footprint on a chip and dissipating excessive amount of energy. Here, we
show an elegant implementation with just two dipole-coupled magneto-tunneling
junctions (MTJ), with magnetostrictive soft layers, fabricated on a
piezoelectric film. The resistance states of the two MTJs (high or low) encode
the bits in the two streams. The first MTJ is driven to a random resistance
state via a current or voltage generating spin transfer torque and/or voltage
controlled magnetic anisotropy, while the second MTJ's resistance state is
determined solely by dipole coupling with the first. The effect of dipole
coupling can be varied with local strain applied to the second MTJ with a local
voltage (~0.2 V) and that varies the correlation between the resistance states
of the two MTJs and hence between the bits in the two streams (from 0% to
100%). This paradigm can be extended to arbitrary number of bit streams. | 1907.07532v1 |
2017-04-26 | Identifying Similarities in Epileptic Patients for Drug Resistance Prediction | Currently, approximately 30% of epileptic patients treated with antiepileptic
drugs (AEDs) remain resistant to treatment (known as refractory patients). This
project seeks to understand the underlying similarities in refractory patients
vs. other epileptic patients, identify features contributing to drug resistance
across underlying phenotypes for refractory patients, and develop predictive
models for drug resistance in epileptic patients. In this study, epileptic
patient data was examined to attempt to observe discernable similarities or
differences in refractory patients (case) and other non-refractory patients
(control) to map underlying mechanisms in causality. For the first part of the
study, unsupervised algorithms such as Kmeans, Spectral Clustering, and
Gaussian Mixture Models were used to examine patient features projected into a
lower dimensional space. Results from this study showed a high degree of
non-linearity in the underlying feature space. For the second part of this
study, classification algorithms such as Logistic Regression, Gradient Boosted
Decision Trees, and SVMs, were tested on the reduced-dimensionality features,
with accuracy results of 0.83(+/-0.3) testing using 7 fold cross validation.
Observations of test results indicate using a radial basis function kernel PCA
to reduce features ingested by a Gradient Boosted Decision Tree Ensemble lead
to gains in improved accuracy in mapping a binary decision to highly non-linear
features collected from epileptic patients. | 1704.08361v1 |
2019-06-24 | Fully Dynamic Spectral Vertex Sparsifiers and Applications | We study \emph{dynamic} algorithms for maintaining spectral vertex
sparsifiers of graphs with respect to a set of terminals $T$ of our choice.
Such objects preserve pairwise resistances, solutions to systems of linear
equations, and energy of electrical flows between the terminals in $T$. We give
a data structure that supports insertions and deletions of edges, and terminal
additions, all in sublinear time. Our result is then applied to the following
problems.
(1) A data structure for maintaining solutions to Laplacian systems
$\mathbf{L} \mathbf{x} = \mathbf{b}$, where $\mathbf{L}$ is the Laplacian
matrix and $\mathbf{b}$ is a demand vector. For a bounded degree, unweighted
graph, we support modifications to both $\mathbf{L}$ and $\mathbf{b}$ while
providing access to $\epsilon$-approximations to the energy of routing an
electrical flow with demand $\mathbf{b}$, as well as query access to entries of
a vector $\tilde{\mathbf{x}}$ such that $\left\lVert
\tilde{\mathbf{x}}-\mathbf{L}^{\dagger} \mathbf{b} \right\rVert_{\mathbf{L}}
\leq \epsilon \left\lVert \mathbf{L}^{\dagger} \mathbf{b}
\right\rVert_{\mathbf{L}}$ in $\tilde{O}(n^{11/12}\epsilon^{-5})$ expected
amortized update and query time.
(2) A data structure for maintaining All-Pairs Effective Resistance. For an
intermixed sequence of edge insertions, deletions, and resistance queries, our
data structure returns $(1 \pm \epsilon)$-approximation to all the resistance
queries against an oblivious adversary with high probability. Its expected
amortized update and query times are $\tilde{O}(\min(m^{3/4},n^{5/6}
\epsilon^{-2}) \epsilon^{-4})$ on an unweighted graph, and
$\tilde{O}(n^{5/6}\epsilon^{-6})$ on weighted graphs.
These results represent the first data structures for maintaining key
primitives from the Laplacian paradigm for graph algorithms in sublinear time
without assumptions on the underlying graph topologies. | 1906.10530v1 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.