decisions made using the invention can be channeled from station 20 to another station or to an output device. the hardware associated with transaction interface 30 may be any one of a number of well - known input / output and other peripheral devices designed for the functions herein described. user interface 40 provides access for a user to the functions of the invention. user interface 40 allows input through a keyboard or other input device, and displays for permitting the user to interact with the invention. user interface 40 is also in communication with decision processor system 60. the hardware associated with user interface 40 may be any number of well - known input / output and other peripheral devices. knowledge base 50 contains the data necessary to perform the different functions of the system. the hardware associated with knowledge base 50 may be any memory device for electronically storing information, such as a digital storage device. knowledge base 50 is conceptually similar to a data base of a standard data processing system, except that it contains a number of artificial intelligence structures to enable decision making. more specifically, knowledge base 50 is arranged as a semantic network of frames. in general, a frame is a knowledge representation structure that represents " objects ", i. e, physical items, facts, and events, in the real world as groups of attributes. a frame contains slots, each of which can have a value. as explained below, these values can include programs to be executed. in a system of frames, frames may inherit values from other frames. the frames within knowledge base 50 may include reasoning programming, which is more accurately described as " application behavior code. " this programming is object - oriented, which means that information is oriented around the objects that the programming manipulates. objects in knowledge base 50 may " behave " and thereby cause data and relationships between objects in the knowledge base to change. to effect such behavior, the programming makes use of demons, which are programs invoked when certain data elements in frames are accessed and determines what to do when certain conditions arise. the programming within knowledge base 50 permits objects to be represented and their interrelationships to be manipulated in a manner analogous to cells of a numeric spreadsheet. this feature is explained in more detail below, in connection with effects processor 62. decision processor system 60 includes two subsystems, including an effects processor 62 and a strategy processor 66, each associated with special programming to accomplish the functions described below. the hardware associated with each processor may be any one of a number of well - known devices capable of executing computer instructions, such as a microprocessor.


" could be either a person operating the equipment or a program that exchanges information with another. furthermore, not all of the data types and functions described below are essential to operation of the invention in its simplest form, and with simple modifications, the invention may accomplish the function of assisting a user in making decisions with some, and not necessarily all of the data types and functions described herein. for example, the decision making function can be used without any selecting methods. it is not necessary to the invention that there be more than one method of decision making or that there be more than one strategy. the strategy programming can be used for managing a set of values only, with no associated choice methods. thus, in the programming of fig. 2, the data types and functions associated with defining multiple methods and multiple strategies, are not essential to the invention and the programming is easily modified to operate without them. as indicated in fig. 2, in general, the programming steps are defining functions and creating data types. an additional step is organizing these data types and functions into a programming structure to control the application of the functions and access to data. fig. 2 is directed to the architectural features of the invention, with functional features and their implementation being further explained in connection with figs. 3 - 7. candidate 200 is a data type that represents the candidates involved in a selection process. candidate 200 is associated with functions from candidate move 210, and a data type, rules 205. candidate 200 is created and maintained by candidate generator 201. candidate generator 201 is a data type that specifies how the candidate pool is created, maintained, and accessed. its internal structure is a list of the generator name, data, and functions from candidate move 210. the data in candidate generator 201 may range from a current candidate pool to a set of functions for determining candidates. candidate generator 201 uses functions defined as candidate move 210 to create and update the candidate pool and to produce each subsequent candidate on demand. candidate generator 201 permits more than one type of candidate generation, thus each candidate generator is identified with a name. candidate generator is an element of method 204. choose 230 determines whether more than one generator will be used during a decision making process, as specified by the current method. candidate move 210, is a set of related user defined functions, which provides an initial pool of candidates or some user defined data structure representing the information required to produce each subsequent candidate on demand. candidate move also provides the means to extract a single candidate from the candidate pool and a method for reducing the candidate pool after a single


provides an initial pool of candidates or some user defined data structure representing the information required to produce each subsequent candidate on demand. candidate move also provides the means to extract a single candidate from the candidate pool and a method for reducing the candidate pool after a single candidate has been extracted. candidate move 210 is created by define candidate move 227, a system function, and is accessed by define candidate generator 225, a system function. state 202, a data type, stores runtime information about a candidate, i. e., its " state " information, both system and user generated. the system created information includes the number assigned to the candidate relative to the current candidate pool and the name of the generator that produced the candidate. state is updated by a system function, put state 226, and is accessible as a parameter from within rules 205 or final action 214. state update 211 is a user defined function, that updates a candidate ' s state information, using a system function put state 226. state update 221 is created by the system function define state update 228, and is accessed as an element of method 204. the preferred embodiment of the invention includes a data type, global context 203, which represents information bearing on the best candidate that is not a property of individual candidates. it is a list of datum keyword and value pairs, initialized by an argument to choose 230. it is accessed by a get system function and updated with a put system function. global context update 212 is a user defined function that makes changes and additions to the global list, using the get and put system function 220 referred to in the preceding paragraph. it is created by define 231, a system defined function, and is accessed as an element of choice method in method 204. method 204, a data type, represents information from which a method for making a choice in a particular way is selected. the internal structure of method 204 is comprised of a number of slots, including at least one of each of the following : a choice name, a method name, a global update function, a candidate generator, a state update function, rules, final action function, rule weights, soft violation inclusion option, scaling option, and approach. the information in these the slots is associated with the data types and functions described herein. rule weights, soft violation inclusion, and the scaling option are discussed below in connection with figs. 3 - 5. method 204 permits choices to be made using one of a multiplicity of possible methods. rules 205 is a data type comprised of at least one set


defined data type, accessed by rules 205, such that rules behave differently depending on strategy parameter values. strategy parameters 208 is created by define strategy parameters 248, a system function. the values within strategy parameters can be obtained interactively from a user or from another program. the strategy feature is further discussed in connection with fig. 5. figs. 3 - 7 illustrate another aspect of the invention, which is a method for using a computer to assist a user in selecting a best choice among alternative choices when making a decision. essentially, figs. 3, 4a, and 4b illustrate the method of making a best choice, given a particular choice method. figs. 5 and 6 illustrate the a method of the invention using strategy selection and learning features. fig. 7 illustrates a method of the invention using a scenario feature. these methods can be implemented with the functions and data types discussed in connection with fig. 2. as indicated above, the " begin " stage of each method can be initiated by a user and the method can be executed interactively, or the method can be programmatic and called or used or both by other programming. the method of fig. 3 assumes that there exists a pool of candidates. step 300 is updating the characteristics of these candidates. a programming structure for implementing step 300 is the global context update 212. step 302 is executing a candidate generation procedure of the computer, such that candidates may be evaluated singularly or in multiples for comparison purposes, during the other steps of the method. candidate generation can range from a simple process that provides the initial pool of candidates as a simple list and extracts elements from the list one at a time, to a more complex process in which candidates are generated on demand using a data structure that represents the candidate pool. the generation of each candidate may be a computationally iterative process, so only as many candidates as required are generated. this latter process can be implemented with the aid of stop rules. however, for some choose options, the entire list of candidates must be generated to do a complete sort of preferred choices or perform the full weighted choose explained below. although not indicated in fig. 3, step 302 may be repeated, i. e, there may be more than one candidate generation. programming for implementing step 302 is described in connection with fig. 2, in particular, candidate generator 201, candidate move 210, and choose 230. whether or not there will be more than one candidate generation is determined by choose 230. step 304 is executing a procedure for selecting a best candidate for resolving the


fig. 2, in particular, candidate generator 201, candidate move 210, and choose 230. whether or not there will be more than one candidate generation is determined by choose 230. step 304 is executing a procedure for selecting a best candidate for resolving the decision. within step 304 are alternative approaches, which are described below in connection with figs. 4a and 4b. an example of programming for implementing step 304 is the function choose 230. step 305 is determining whether there are any final action functions, such as final action 214. if there are, step 306 is performing the final action. if there are no final actions, step 308 returns the best candidate to the user. figs. 4a and 4b illustrate substeps of step 304. as will be explained in connection with each figure, the invention provides two choice approaches : a hierarchical approach and a weighted choose approach. regardless of the approach, it is assumed that a pool of candidates with updated information is available from the data types and functions described above. furthermore, if rules are to have rule weights, the rules are sorted accordingly. both approaches include steps involving the application of hard and soft elimination rules. if a hard elimination rule fails for a candidate, the candidate is eliminated and the next candidate is considered. soft elimination rules are applied to each candidate that has passed the hard elimination rules. unlike hard elimination rules, soft elimination rules may continue to be applied to a candidate, regardless of whether a failure has already occurred. a soft elimination rule score is accumulated for each candidate by adding in the rule weight of each rule passed. in addition to receiving scores, the candidates are assigned to one of two groups : a group containing candidates that have passed all soft elimination rules applied so far, and a group containing candidates that have failed at least one soft elimination rule. programming to implement the rules is described above in connection with rules 205, method 204, and choose 230. the particular approach for decision making may include scaling with respect to soft elimination rules. if scaling is to be applied, the final soft elimination score in multiplied by the number of candidates currently being considered. this allows the soft elimination score to be combined on an equal basis with the subsequent comparison rule score. an example of implementation of such scaling is an element, such as a flag, in method 204. both approaches include steps for applying stop rules. if a stop rule succeeds for a candidate, the decision making process stops. one example of a stop rule is when the latest best candidate is sufficient. another example is when the decision making has taken too


invention with the strategy selection features involves a first step, step 510, of adopting a strategy. when a strategy is adopted, the parameter values and choice methods of that strategy become the current values and choice methods. step 512 is executing the decision making steps of fig. 3 to choose a best candidate. step 514 determines if the best candidate is acceptable. if it is, step 516 is using the best candidate in other programming or as desired by the user. steps 518 and 520 of fig. 5 illustrate another feature of the invention, which may be used during the development stage of the decision making system. this is a learning feature, which is invoked by the user after a decision making operation has failed to produce the desired result. in general, the learning feature is a rule weight adjusting feature in connection with the weighted choose method, so that the candidate who is the user ' s best choice will receive the highest score, and thereby improve the knowledge base. the learning steps are iterative for each " rule instance ", i. e., each part of the weighted choose method in which a particular rule was evaluated for the entire set of candidates surviving elimination. a rule instance is the rule weight and a list of candidate / rank weight pairs. step 518 determines whether this learning feature is to be invoked. if so, step 520 is performing it. the substeps of step 520 are illustrated in fig. 6. it is assumed that the programming has already saved each candidate and its state information, including the total score for each candidate, and each rule instance. step 610 is getting a rule instance. step 612 ensures that the learning steps continue for each rule instance. step 614 is determining the relationship between the current rule and the current candidate ' s total, t. for each rule, there are three status categories : ( 1 ) every candidate that has a higher current t than the desired candidate is ranked higher by the current rule, or ( 2 ) every candidate that has a higher current t than the desired candidate is ranked lower by the current rule, or ( 3 ) neither category ( 1 ) nor ( 2 ) exists. according to the category in which a rule falls, the remaining steps increase or decrease that rule ' s weight or set the rule aside. if the rule falls within category 3, step 618 sets the rule aside. steps 620 - 626 ensures that if the rule is set aside, after any rule that falls within category ( 1 ) or ( 2 ) has had its weight adjusted, the set aside rules


pool and dividing that sum into the largest delta. step 644 is recomputing delta as the minimum of the scaled lo and sc. step 646 is determining whether the rule is a category 1 rule. if so, step 648 is computing a new rule weight as the old rule weight minus delta. if the rule is not in category 1, which implies that it is in category 2, the rule weight is the old rule weight plus delta. step 652 recalculates t for each candidate, and checks the pool of set aside rules, as indicated above. after every rule instance has been evaluated by steps 614 - 652, step 654 is determining whether the desired candidate has an improved position in a sorted list of candidate totals than it did with the original rule weights. if so, step 656 returns the adjusted rule weights. referring again to fig. 5, if the learning feature is not invoked, step 510 - 514 are repeated until an acceptable candidate is determined. fig. 7 illustrates a feature of the invention that integrates features of the decision processing system of fig. 1. in particular, fig. 7 illustrates a method for generating trial solutions using different strategies. the method may be implemented using the apparatus and programming discussed above in connection with decision processor 60 and knowledge base 50. step 710 is entering an " effects mode " of a computer system programmed with constraint propagation capabilities. step 712 is determining whether a new scenario is to be created. if a new scenario is to be created, step 714 is creating the scenario and associating a particular strategy with the scenario. if no new scenario is to be created, step 716 is determining whether a previously selected scenario is to be processed. if not, step 718 is leaving the effects mode and selecting a solution. referring again to step 716, if a previous scenario is to be used, step 720 is selecting a scenario. once a scenario has been created or selected, step 722 is entering that scenario, which implies the adoption of an accompanying strategy. step 724 is solving the problem by entering the decision making aspects of the invention. the programming discussed above in connection with figs. 3, 4a, and 4b are directed to this step. although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. various modifications of the disclosed embodiment, as well as alternative embodiments, of the invention will become apparent to persons skilled in the


d - f - a collection of similar information stored in a file, such as a database of addresses. this information may be created and stored in a database management system ( dbms ). - slang. to find and correct equipment defects or program malfunctions. - the pre - defined configuration of a system or an application. in most programs, the defaults can be changed to reflect personal preferences. - the main directory of the user interface. desktops usually contain icons that represent links to the hard drive, a network ( if there is one ), and a trash or recycling can for files to be deleted. it can also display icons of frequently used applications, as requested by the user. - desktop publishing - the production of publication - quality documents using a personal computer in combination with text, graphics, and page layout programs. - a list of files stored in the computer. - two distinct types. the names refer to the media inside the container : - a hard disc stores vast amounts of data. it is usually inside the computer but can be a separate peripheral on the outside. hard discs are made up of several rigid coated metal discs. currently, hard discs can store 15 to 30 gb ( gigabytes ) - a floppy disc, 3. 5 " square, usually inserted into the computer and can store about 1. 4 megabytes of data. the 3. 5 " square “ floppies ” have a very thin, flexible disc inside. there is also an intermediate - sized floppy disc, trademarked zip discs, which can store 250 megabytes of data. hard disc drive - disk drive - the equipment that operates a hard or floppy disc. - the instruction manual for a piece of hardware or software. - represents an ip ( internet protocol ) address or set of ip addresses that comprise a domain. the domain name appears in urls to identify web pages or in email addresses. for example, the email address for the first lady is firstname. lastname @ example. org, “ whitehouse. gov ” being the domain name. each domain name ends with a suffix that indicates what “ top level domain ” it belongs to. these are : “. com ” for commercial, “. gov ” for government, “. org ” for organization, “. edu ” for educational institution, “. biz ” for business, “. info ” for information, “. tv ” for television, “. ws ” for website. domain suffixes may also indicate the country in which the domain is registered.


today is a date in history to note for humankind and for our understanding of the universe. scientists at european organization for nuclear research ( cern ) have announced that they believe they have found the elusive higgs boson – the particle that elementary particles interact with to gain mass. the search began nearly 50 years ago with the invention of the mechanism for mass generation by phil anderson in the context of superconductivity. its existence as a sub - atomic particle was first hypothesized by peter higgs. on behalf of the liberal party i would like to congratulate the more than 100 canadian researchers who have been working for many decades on this international collaboration at cern. while research into high energy physics certainly does not come cheaply, and we don ’ t always know immediately what practical uses the results of that research will have, understanding the universe we live in is an important activity that has never failed to give us tools by which we might move humanity forward and improve the lives of billions. canada has a tremendous history of contributing to basic research that has revolutionized the world. the most famous example is perhaps the discovery of insulin by dr. frederick banting and his research assistant charles best working at the university of toronto. sadly under stephen harper the government of canada is steadily walking away from funding basic research. for instance, the natural research council has been ordered to turn away from early stage research and focus instead on direct commercial applications. granting councils like the natural sciences and engineering research council of canada ( nserc ) have increasingly lost funding for basic research. since 2006 funding for discovery grants has fallen from $ 420 million to $ 360 million. i ’ m sure that today we will all see and read many stories about the years of effort it has taken to find the higgs boson. as we reflect on the significance of this accomplishment, i hope we take a moment to consider the thousands of basic research groups across this country. it is the curiosity and dedication of these researchers, along with funding to test their ideas, and heeding their expert advice and warnings that will help us build a healthier, more prosperous civilization for everyone. - ted hsu liberal science and technology critic


of or pertaining to pluto ; plutonian ; hence, pertaining to the interior of the earth ; subterranean. of, pertaining to, or designating, the system of the plutonists ; igneous ; as, the plutonic theory. ( ploo tahn ' ic ) - igneous rocks that form from the cooling of magma in the interior of a planet or asteroid. describes igneous rocks formed deep beneath the earth ' s surface plutonic rocks are igneous rocks that crystallize below the eartha€™s surface. they are characterized by visible crystals arranged in a three - dimensional interlocking mosaic. of igneous rock that has solidified beneath the earth ' s surface ; granite or diorite or gabbro related to the cooling of molten materials within the earth. a pluton is a body of hot material that rises within the earth because it is less dense that the material around it. when this material cools before breaking the surface, it forms plutonic, or intrusive, rocks. an igneous rock, or relating to igneous rock, that crystallized below the surface of the earth. the crystals in a plutonic rock are the size of grains of sugar or larger. pertaining to igneous rock formed at great depth. a plutonic rock is coarse - grained due to slow cooling underground. refers to rocks of igneous origin that have come from great depth. applies to igneous rocks formed beneath the surface of the earth ; typically with large crystals due to the slowness of cooling. synonym of intrusive. antonym of volcanic. eruptive or igneous rock consolidated at depth. having to do with a class of intrusive igneous rocks that have solidified far below the earth ' s surface ; or or having to do with the theory that the present condition of the earth ' s crust is mainly due to igneous action. [ ahdos


computer hacking and security with the rapid growth of the worldwide internet user base, online transactions are believed to reach well over a trillion dollars in the next three years. with stakes this high, it makes sense for all parties involved to secure the internet. haphazard handling of financial and personal information can lead to the internet being constantly associated with fraud and privacy abuses instead of being a viable commerce medium. the goal for higher security starts with the individual user. the term " hacker " has been around for a while. it originally referred to a person not well versed with a computer trying different things to accomplish a task. to hack was to figure out something through sheer trial and error or logical deduction. today, a hacker described as a person who breaks into computers for various reasons. crackers and script - kiddies are two other more commonly used terms describing those involved in the break in or disruption of an online service. security problems can occur in any networked environment. many of the problems are related to the exploitation of the original design of the tcp / ip suite of internetworking protocols, but the majority are due to configuration or operator errors. hackers are not just looking for websites or government computers to hack - utility grids, emergency information systems, controls for dams and locks, financial information, inter - banking information, military communications and much more sensitive information travels on the internet and other communication networks. in broad terms, security threats can be classified as active and passive. active hacking : active attacks involve the modification of transmitted data and attempts to gain unauthorized access to systems. data communication is based on a set of handshakes to ensure the smooth and reliable flow of information. a hacker that is between a client and a server and is able to spoof ( illegally duplicate ) the ip address and sequence numbers, can attack either machine in several ways. the hacker can disable one of the machines and take the identity of the other, or the hacker can mimic either machine and carry on conversations impersonating the other. a hacker could also attach additional information to a client request and strip the corresponding additional response from the packet before forwarding the remaining response to the client ' s original request. all this while having access to information that is assumed to be going back and forth between two ' trusted ' systems. computer viruses and trojans are also examples of active attacks. they can disable machines or in the case of trojans allow malicious hackers access to senstive information by creating a back door. passive hacking : passive attacks have to do with


we present the molecular beam epitaxy fabrication and optical properties of complex gaas nanostructures by droplet epitaxy : concentric triple quantum rings. a significant difference was found between the volumes of the original droplets and the final gaas structures. by means of atomic force microscopy and photoluminescence spectroscopy, we found that a thin gaas quantum well - like layer is developed all over the substrate during the growth interruption times, caused by the migration of ga in a low as background. keywords : molecular beam epitaxy ; droplet epitaxy ; gaas nanostructures ; photoluminescence the fabrication of semiconductor quantum nanostructures based on self - assembly has deeply attracted the research community because of the interest in fundamental physics and the potential applications of these systems as building blocks for novel devices and quantum information technologies [ 1 - 3 ]. in particular, quantum rings, a special class of semiconductor nanostructures, have been investigated since they manifest a quantum - interference phenomenon, known as the aharonov – bohm ( ab ) effect, and have also been applied for the fabrication of optoelectronic devices [ 5 - 7 ]. therefore, the ability in the production of quantum ring systems has a great relevance in the nanotechnology field. during the last 15 years, molecular beam epitaxy ( mbe ) has been successfully employed for the fabrication of semiconductor nanoscopic rings, without the use of any lithographic step [ 8 - 11 ]. based on droplet epitaxy ( de ) [ 12, 13 ], we recently demonstrated the fabrication and discussed the growth of gaas concentric multiple quantum rings. the innovation in our growth protocol, compared with the standard de, resides in the multiple steps used for the droplets crystallization. normally the crystallization of nanometer - sized ga droplets, automatically formed at the substrate surface after irradiation of ga, has been achieved by supplying an as flux until the complete consumption of ga atoms. on the contrary, we introduced many pulsed arsenization steps at different substrate temperatures, opening the possibility for the fabrication of more complex gaas nanostructures. the partial crystallization of the available ga inside the droplets allows changes in the subsequent as supply condition ( arsenic bep and substrate temperatures ), adding an important degree of freedom in the fabrication technique. here, we will discuss the formation of concentric triple quantum rings ( ctqrs ), describing the morphological features by means of atomic force microscopy (


( arsenic bep and substrate temperatures ), adding an important degree of freedom in the fabrication technique. here, we will discuss the formation of concentric triple quantum rings ( ctqrs ), describing the morphological features by means of atomic force microscopy ( afm ) analysis, and we will show the optical properties of the system, investigated by photoluminescence ( pl ) spectroscopy. interestingly, we found that the volume of the final gaas nanostructure is much lower than the expected value, estimated from the initial amount of supplied ga. this discrepancy is justified in terms of ga atoms diffusion from the droplets to high distance onto the substrate surface during the growth interruption steps of the procedure. this explanation is supported by the presence of an additional peak in the pl spectra consistent with the emission of a quantum well - like thin layer of gaas formed all over the substrate. the growth experiments were performed in a conventional gen ii mbe system using epi - ready gaas ( 001 ) substrates. after the growth of a 500 - nm - thick gaas buffer layer and of a 200 - nm - thick al0. 3ga0. 7as barrier layer at 580°c, the substrate temperature was decreased to 350°c and the as valve closed until the background pressure was below 1 × 10−9 torr. at the same temperature, a ga molecular beam equivalent to the formation of 10 ml of gaas in the presence of as was supplied to the substrate surface, for the droplets formation. after that, the substrate temperature was decreased to 250°c and an as bep of 8 × 10−7 torr was supplied for 20 s for the partial crystallization of the original droplets into gaas. finally, the substrate temperature was increased to 300°c and the sample surface was irradiated by the same as bep ( 8 × 10−7 torr ) for 20 min, to ensure the complete reaction of metallic ga with as. it is worth mentioning that a growth interruption time of around 1 h was used to reach the thermal stability of the sample after each change of the substrate temperature. after the growth, the samples were taken out of the chamber for the morphological analysis by afm and optical investigation by pl. three samples were prepared : sample a by stopping the growth just after the ga supply ; sample b after completely performing the described procedure ; and sample c by burying the gaas nanostructure in al0. 3ga0. 7as and annealing at 650°c in as atmosphere for


the growth just after the ga supply ; sample b after completely performing the described procedure ; and sample c by burying the gaas nanostructure in al0. 3ga0. 7as and annealing at 650°c in as atmosphere for the optical measurements. photoluminescence spectra of sample c were measured at t = 15 k using a green laser ( λexc = 532 nm ) as excitation source with a power density pexc = 10 w / cm2 and recorded by a peltier - cooled ccd camera. results and discussion in fig. 1a and 1b, we show the afm images of sample a, where the growth was stopped just after the deposition of ga and sample b, where the entire procedure was performed. the ga supply clearly resulted in the formation of nanometer - sized, nearly hemispherical ga droplets. their average diameter and height were around 80 and 35 nm, respectively, while the density was estimated to be around 8 × 108 cm−2. at the end of the procedure, clear ctqrs structures with good rotational symmetry appeared, with inner, middle and outer ring diameters of around 80, 140 and 210 nm, respectively, while heights were around 7 nm for the inner rings, 4 nm for middle rings and 3 nm for the outer rings. these structures showed an elongation of around 11 % along the [ 0 – 11 ] direction, which might be due to the anisotropic diffusion of ga on gaas ( 001 ) surface. it is worth noticing that the inner rings showed nearly the same diameter to that of the original ga droplet and that the density of the final gaas structures was equal to that of the original droplets, confirming that all ga droplets transformed into gaas triple rings at the end of the procedure. as already discussed in ref., the formation of the inner rings comes from the crystallization of the droplets edge, thus explaining the identity between droplets and inner rings diameters. on the contrary, middle and outer rings appear caused by the subsequent as supplies, as a result of the interplay between as adsorption and ga migration from the droplets. fig. 1c shows the cross - sectional height profile for sample a ( black line ) and b ( red line ) obtained from the afm images. it is important to point out that there is a significant difference between the number of ga atoms initially supplied, corresponding to the equivalent amount of 10 mls, and the number of ga atoms, evaluated to be equivalent to around 3


from the afm images. it is important to point out that there is a significant difference between the number of ga atoms initially supplied, corresponding to the equivalent amount of 10 mls, and the number of ga atoms, evaluated to be equivalent to around 3 – 4 mls, inside the final structure. this difference suggests that only a fraction of the initially supplied ga atoms effectively concur to the formation of the 3d nanostructures, while the other part, estimated to be around 6 – 7 mls, might be consumed in another process. the reason for this discrepancy might be found considering our experimental procedure for the formation of ctqrs. as mentioned before, the three main steps of the growth are performed at different temperatures : 350°c for the droplets formation, 250°c for the first as supply and 300°c for the second as supply. to establish the thermal equilibrium of the substrate, we observed 1 h growth interruption times after each change of the substrate temperature. during these waiting times, a portion of the ga atoms stored in the droplets might be consumed to form a 2d gaas thin layer all over the substrate. we believe this phenomenon to be caused by a slow 2d crystallization of ga atoms diffusing from the droplets, even in the absence of an intentional as supply. indeed, an as background pressure of around 1 × 10−9 torr is present during the whole procedure, thus providing the unintentional as pressure needed for the partial crystallization of ga atoms. as we recently found in similar systems, a slow gaas crystallization all over the substrate might take place in case of very low as supply to the ga droplets. in these conditions of very low as flux, the surface mobility of ga atoms is so large that an uniform layer of gaas might be formed all over the substrate surface. in a capped sample, embedded in an al0. 3ga0. 7as barrier, this layer can act as a quantum well, confining carriers and eventually being optically active. in order to check the optical quality of ctqrs and to confirm the presence of a thin quantum well - like gaas layer all over the substrate coming from the unintentional crystallization of a certain amount of ga atoms during the procedure, we performed pl investigations. the same structure of sample b was therefore grown on another sample ( sample c ) and embedded in an al0. 3ga0. 7as barrier layer. figure 2 shows the pl spectra of sample c excited at 15 k by a


pl investigations. the same structure of sample b was therefore grown on another sample ( sample c ) and embedded in an al0. 3ga0. 7as barrier layer. figure 2 shows the pl spectra of sample c excited at 15 k by a green laser ( λexc = 532 nm ) with a power density pexc = 10 w / cm2 and recorded by a peltier - cooled ccd camera. in the region where the emission from quantum - confined gaas structures is expected, two peaks, respectively named peak 1 at 1. 55 ev and peak 2 at 1. 76 ev, appeared. a calculation on the electronic structure for the ctqrs was performed in the framework of the effective mass approximation [ 17 - 20 ], allowing us to attribute peak 1 to the emission of the localized states within the ctqrs. on the other hand, on the basis of the same theoretical predictions, peak 2 can be safely assigned to a 2d gaas quantum well ( qw ), which appeared all over the substrate during the procedure. as already discussed, only a fraction of the total supplied ga is effectively crystallized to form the triple rings, while the remaining 6 – 7 mls of ga atoms concur to the formation of a 2d layer of gaas, as described above. within the effective mass approximation, a 6 – 7 mls - thick gaas qw is expected to emit at 1. 76 ev, in excellent agreement with the observed peak 2 feature. we believe that the presence of this 2d layer might be a general feature in the samples grown with our multiple steps de, by observing growth interruption times. figure 1. afm 2 × 2 micron images of sample a ( a ) and b ( b ). insets show a 3d - magnified picture of a single structure. cross sectional height profiles of a single ga droplet and concentric triple quantum ring ( c ) figure 2. pholuminescence spectra of ctqrs recorded at 15 k. gaas and al0. 3ga0. 7as peaks appeared at 1. 52 and 1. 90 ev, respectively. between them additional two features appeared, at 1. 55 ev ( peak 1 ) and at 1. 76 ev ( peak 2 ) we presented the growth and the optical properties of gaas ctqrs fabricated by de. at the end of our multistep procedure, ga droplets are transformed into these complex nanostructures. we found a significant difference in the volume of the final structure compared


and the optical properties of gaas ctqrs fabricated by de. at the end of our multistep procedure, ga droplets are transformed into these complex nanostructures. we found a significant difference in the volume of the final structure compared to the initially supplied amount of ga. we explain this discrepancy in terms of ga diffusion all over the substrate during the growth interruption steps of the experiments, caused by the residual as partial pressure in the chamber. this picture is strongly supported by the presence of a high - energy peak in the pl, which is consistent with the presence of a thin gaas quantum well on the substrate. this work was partially supported by the cariplo foundation ( prj. quadis2 – no. 2008 - 3186 ). this article is distributed under the terms of the creative commons attribution noncommercial license which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author ( s ) and source are credited. science. 2000, 290 : 2282. coi number [ 1 : cas : 528 : dc % 2bd3cxptfsnu7s % 3d ] ; bibcode number [ 2000sci... 290. 2282m ] pubmed abstract | publisher full text science. 2003, 301 : 809. coi number [ 1 : cas : 528 : dc % 2bd3sxmtvgqsrc % 3d ] ; bibcode number [ 2003sci... 301.. 809l ] pubmed abstract | publisher full text phys. rev. b. 2003, 67 : 121307. bibcode number [ 2003phrvb.. 67l1307s ] publisher full text phys. rev.. 1959, 115 : 485. bibcode number [ 1959phrv.. 115.. 485a ] publisher full text appl. phys. lett.. 2006, 89 : 183102. bibcode number [ 2006apphl.. 89r3102m ] publisher full text appl. phys. lett.. 2009, 94 : 171102. bibcode number [ 2009apphl.. 94q1102w ] publisher full text appl. phys. lett.. 2009, 95 : 071908. bibcode number [ 2009apphl.. 95g1908w ] publisher full text


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. tue dec 25 05 : 43 : 29 gmt 2007 by gw fourmyle well, pilgrims - - you ' ve a few ' anomalies ', hardly 1. start with the galaxy chains, loops around huge voids - - sure, put an ' inflationary - theory ' band - aid on it. yeah. i suggest an elegant solution - - as - entropy has been produced on earth, and + entropy, i. e. ' s ' is rather obvious at reaching far beyond its initial thermodynamic concept - - seems to me s is the ' property - of - mass ', and ' g '? a myth. sure, mass curves space / time, i contend that is an ' s ' function. ' disorder - with - respect - to mass '. realizing dr. e. was doing his work, on a massive planet, in a massive stellar system, one would expect these ' anomalies ', as probes exit, or universes of infinite mass will bear infinite s - - - fortunately infinite - s must be equal. extrapolating calculations made in a burning house to all houses? here i see massive ' error - of - reasoning '. the stunning aspect is if s may ' disorder ' space / time? why not living - systems? the simple experiment, for most, is simply looking in a mirror, reading the news, or fighting cancer - - - too long, physics has only dealt in ' dead - stuff ' - - - there is more - - - all comments should respect the new scientist house rules. if you think a particular comment breaks these rules then please use the " report " link in that comment to report it to us. if you are having a technical problem posting a comment, please contact technical support.


when an electron collides with an atom or ion, there is a small probability that the electron kicks out another electron, leaving the ion in the next highest charge state ( charge q increased by + 1 ). this is called electron - impact ionization and is the dominant process by which atoms and ions become more highly charged. the rate equation is given by : e - + a ( q ) e - + e - + a ( q + 1 ). from energy conservation, it is clear that the initial energy of the incident electron must be larger than the ionization potential of the electron being removed. theorists have found electron impact ionization cross sections difficult to calculate from first principles, even for relatively simple systems like hydrogen - like ( one electron ) and helium - like ( two electron ) ions. there has been recent progress in developing a phenomenological theory by dr. yong - ki kim here at nist. a simple empirical formula for calculating electron impact ionization cross sections was developed by w. lotz over 25 years ago. it is not very accurate, but it does give experimentalists a useful qualitative picture. radiative recombination is a process which takes place when a positively charged ion captures an electron to one of its bound orbits with a simultaneous emission of a photon : e - + a ( q + ) a ( q - 1 ) + photon in the dielectronic recombination process the energy which becomes available during the capture process is carried away by the promotion of a bound electron to another bound orbit : e - + a ( q + ) a ( q - 1 ) * * a ( q - 1 ) + photon in the second step of the dielectronic recombination process a photon is emitted characteristic to the doubly excited state ( * * ) of the q - 1 times ionized ion. the dielectronic recombination is a resonant process, because of the discrete energy nature of the bound electron orbits. both radiative and the dielectronic recombination are important capture processes which play a dominant role in determining the charge state balance of highly ionized astrophysical and laboratory plasmas. in a recent investigation carried out with our ebit, scandium - like and titanium - like barium ions were created, trapped, and excited. x - ray peaks arising from both radiative recombination and dielectronic recombination were studied simultaneously. in the


, scandium - like and titanium - like barium ions were created, trapped, and excited. x - ray peaks arising from both radiative recombination and dielectronic recombination were studied simultaneously. in the dr process a 2p electron was promoted to the 3d orbital. one of the m - shell electrons of the recombined ion subsequently decayed radiatively to the 2p vacancy, and emitted an x - ray of energy almost twice the incident kinetic energy of the projectile electron. comparison with theoretical estimates showed a favorable agreement with the data. the theoretical calculations were carried out by the theory group of the university of connecticut ( mclaughlin and hahn ). the measurement of excited - state lifetimes is complementary to measuring transition wavelengths as a way of studying atomic structure. although the lifetimes are determined by the same wavefunctions as the energy levels the measurements of the atomic decays carry different information since they are sensitive to the long - range behavior of the wavefunctions. the knowledge of the lifetimes also has important practical applications. they are critical in the density diagnostics of laboratory and astrophysical plasmas. the principle of measuring lifetimes with an ebit lies in the periodic fast switching of different voltages in the machine. since the ions are created and excited with the same beam of electrons, by changing the electron beam energy one can selectively exclude certain levels from being excited. this can simply be done by setting the electron beam energy below the excitation threshold of the level to be excluded. without further excitation the time dependence of the emitted photon signal carries the information about the lifetime of the level. after a certain period of time ( determined by the lifetime of the level ) the electron beam energy is set to be above the excitation threshold to repopulate the level and repeat the sequence. an alternative method for measuring lifetimes with an ebit is to switch off the electron beam completely, take data, and turn the beam back again to re - excite the ions in the trap. while the electron beam is off, the ions remain trapped by the magnetic field. the lifetime range that can be measured with an ebit is determined by the capabilities for the fast switching of voltages. in principle the 10 ns to 10 ms lifetime range can be addressed by this method. since this lifetime range is only partially covered by other methods the ebit is a unique tool for measuring the lifetime of long living metastable levels. in a recent experiment we have measured the


new view of superconductivitycategory : science & technology posted : may 31, 2012 05 : 22pm the ultimate goal for many materials scientists and the field of electronics is the creation of room - temperature superconductors. these, thus far, undiscovered material are able to carry electric currents with no resistance and no energy loss, like their low temperature brethren. the key to this ability is the formation of cooper pairs, which scientists do not fully understand at the moment. researchers at berkeley lab have recently done an interesting experiment to see how cooper pairs form, and this research may lead to a new understanding of the pairs. cooper pairs are, essentially, electrons that have overcome their usual electromagnetic repulsion so they may travel together. in this coupled state the electrons have less energy than they would separately, but this energy they keep as they travel, which is what makes a material a superconductor. to understand how the cooper pairs form, the researchers decided to break some up using a pump - probe technique. an initial pumping laser pulse hits the cooper pair, causing it to split into two higher energy quasiparticles which the probing laser pulse interacts with. the probing laser pulse captures some information from these quasiparticles, including their momentum and energy. the data show the momentum of the quasiparticles and the energy of the pumping pulse influence how quickly the cooper pair reforms. this could be an indication of what keeps the pairs together. naturally, further study has to be done. only one high temperature superconductor was used for this study, and likely the researchers will want to use additional samples. also the light sourced used for this test is only able to produce low energy pulses. for this experiment though, that limit proved useful as it allowed for better momentum resolution. future experiments will likely want to explore other, potentially more intriguing, energy levels however.


ether is a class of organic compounds which contain an ether group — an oxygen atom connected to two ( substituted ) alkyl or aryl groups — of general formula r – o – r '. a typical example is the solvent and anesthetic diethyl ether, commonly referred to simply as " ether " ( ethoxyethane, ch3 - ch2 - o - ch2 - ch3 ). cannot form hydrogen bonds among each other, resulting in a relatively low boiling point comparable to that of the analogous alcohols. however, the differences in the boiling points of the ethers and their isometric alcohols become smaller as the carbon chains become longer, as the hydrophobic nature of the carbon chain becomes more predominant over the presence of hydrogen bonding. ethers are slightly polar as the coc bond angle in the functional group is about 110 degrees, and the c - o dipoles do not cancel out. ethers are more polar than alkenes but not as polar as alcohols, esters or amides of comparable structure. however, the presence of two lone pairs of electrons on the oxygen atoms makes hydrogen bonding with water molecules possible, causing the solubility of alcohols ( for instance, butan - 1 - ol ) and ethers ( ethoxyethane ) to be quite dissimilar. cyclic ethers such as tetrahydrofuran and 1, 4 - dioxane are totally miscible in water because of the more exposed oxygen atom for hydrogen bonding as compared to aliphatic ethers. ethers can act as lewis bases. for instance, diethyl ether forms a complex with boron compounds, such as boron trifluoride diethyl etherate ( bf3. oet2 ). ethers also coordinate to magnesium in grignard reagents ( rmgbr ). in the iupac nomenclature system, ethers are named using the general formula " alkoxyalkane ", for example ch3. if the ether is part of a more complex molecule, it is described as an alkoxy substituent, so - och3 would be considered a " methoxy - " group. the simpler alkyl radical is written in front, so ch3 would be given as methoxy ). the nomenclature of describing the two alkyl groups and appending " ether ", e. g. " ethyl methyl ether " in the example above, is a trivial usage ethers are not to