Study of a Nonlocal Density scheme for electronic--structure calculations

An exchange-correlation energy functional beyond the local density approximation, based on the exchange-correlation kernel of the homogeneous electron gas and originally introduced by Kohn and Sham, is considered for electronic structure calculations of semiconductors and atoms. Calculations are carried out for diamond, silicon, silicon carbide and gallium arsenide. The lattice constants and gaps show a small improvement with respect to the LDA results. However, the corresponding corrections to the total energy of the isolated atoms are not large enough to yield a substantial improvement for the cohesive energy of solids, which remains hence overestimated as in the LDA.Comment: 4 postscript figure

Grip-Pattern Recognition for Smart Guns

This paper describes the design, implementation and evaluation of a user-verification system for a smart gun, which is based on grip-pattern recognition. An existing pressure sensor consisting of an array of 44 x 44 piezoresistive elements has been used. An interface has been developed to acquire pressure images from the sensor. The values of the pixels in the pressure-pattern images are used as inputs for a verification algorithm, which is currently implemented in software on a computer. The verification algorithm is based on a likelihood-ratio classifier for Gaussian probability densities. First results indicate that it is possible to use grip-pattern recognition for biometric verification, when allowing a certain false-rejection and false-acceptance rate. However, more measurements are needed to give a more reliable indication of the systems performance

Pitfall of the Detection Rate Optimized Bit Allocation within template protection and a remedy

One of the requirements of a biometric template protection system is that the protected template ideally should not leak any information about the biometric sample or its derivatives. In the literature, several proposed template protection techniques are based on binary vectors. Hence, they require the extraction of a binary representation from the real- valued biometric sample. In this work we focus on the Detection Rate Optimized Bit Allocation (DROBA) quantization scheme that extracts multiple bits per feature component while maximizing the overall detection rate. The allocation strategy has to be stored as auxiliary data for reuse in the verification phase and is considered as public. This implies that the auxiliary data should not leak any information about the extracted binary representation. Experiments in our work show that the original DROBA algorithm, as known in the literature, creates auxiliary data that leaks a significant amount of information. We show how an adversary is able to exploit this information and significantly increase its success rate on obtaining a false accept. Fortunately, the information leakage can be mitigated by restricting the allocation freedom of the DROBA algorithm. We propose a method based on population statistics and empirically illustrate its effectiveness. All the experiments are based on the MCYT fingerprint database using two different texture based feature extraction algorithms

Ab initio study of a mechanically gated molecule: From weak to strong correlation

The electronic spectrum of a chemically contacted molecule in the junction of a scanning tunneling microscope can be modified by tip retraction. We analyze this effect by a combination of density functional, many-body perturbation and numerical renormalization group theory, taking into account both the non-locality and the dynamics of electronic correlation. Our findings, in particular the evolution from a broad quasiparticle resonance below to a narrow Kondo resonance at the Fermi energy, correspond to the experimental observations.Comment: 4 pages, 3 figure

A Self-consistent DFT+DMFT scheme in the Projector Augmented Wave : Applications to Cerium, Ce2O3 and Pu2O3 with the Hubbard I solver and comparison to DFT+U

An implementation of full self-consistency over the electronic density in the DFT+DMFT framework on the basis of a plane wave-projector augmented wave (PAW) DFT code is presented. It allows for an accurate calculation of the total energy in DFT+DMFT within a plane wave approach. In contrast to frameworks based on the maximally localized Wannier function, the method is easily applied to f electron systems, such as cerium, cerium oxide (Ce2O3) and plutonium oxide (Pu2O3). In order to have a correct and physical calculation of the energy terms, we find that the calculation of the self-consistent density is mandatory. The formalism is general and does not depend on the method used to solve the impurity model. Calculations are carried out within the Hubbard I approximation, which is fast to solve, and gives a good description of strongly correlated insulators. We compare the DFT+DMFT and DFT+U solutions, and underline the qualitative differences of their converged densities. We emphasize that in contrast to DFT+U, DFT+DMFT does not break the spin and orbital symmetry. As a consequence, DFT+DMFT implies, on top of a better physical description of correlated metals and insulators, a reduced occurrence of unphysical metastable solutions in correlated insulators in comparison to DFT+U.Comment: 19 pages, 9 figures. This is an author-created, un-copyedited version of an article accepted for publication in Journal of Physics: Condensed Matter. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at doi: 10.1088/0953-8984/24/7/07560

Matching hand radiographs

Biometric verification and identification methods of medical images can be used to find possible inconsistencies in patient records. Such methods may also be useful for forensic research. In this work we present a method for identifying patients by their hand radiographs. We use active appearance model representations presented before [1] to extract 64 shape features per bone from the metacarpals, the proximal, and the middle phalanges. The number of features was reduced to 20 by applying principal component analysis. Subsequently, a likelihood ratio classifier [2] determines whether an image potentially belongs to another patient in the data set. Firstly, to study the symmetry between both hands, we use a likelihood-ratio classifier to match 45 left hand images to a database of 44 (matching) right hand images and vice versa. We found an average equal error probability of 6.4%, which indicates that both hand shapes are highly symmetrical. Therefore, to increase the number of samples per patient, the distinction between left and right hands was omitted. Secondly, we did multiple experiments with randomly selected training images from 24 patients. For several patients there were multiple image pairs available. Test sets were created by using the images of three different patients and 10 other images from patients that were in the training set. We estimated the equal error rate at 0.05%. Our experiments suggest that the shapes of the hand bones contain biometric information that can be used to identify persons

Density functional theory calculations of the transition states for hydrogen exchange and dehydrogenation of methane by a Brönsted zeolitic proton

D. functional and semiempirical (MNDO) theories are used to det. transition states and the corresponding activation barriers of hydrogen exchange and dehydrogenation of methane catalyzed by a protonated zeolite cluster model. The nonlocal d. functional activation barriers were found to be 125 and 343 kJ/mol for hydrogen exchange and dehydrogenation, resp. From the imaginary frequency of one of the transition state Eigen modes, the reaction coordinates were deduced. Addnl., from the activation barrier and vibration, rotation, and translation partition functions, reaction rate consts. have been evaluated using transition state reaction rate theory. [on SciFinder (R)