Supervised Hashing for Retrieval of Multimodal Biometric Data

Biometric systems commonly utilize multi-biometric approaches where a person is verified or identified based on multiple biometric traits. However, requiring systems that are deployed usually require verification or identification from a large number of enrolled candidates. These are possible only if there are efficient methods that retrieve relevant candidates in a multi-biometric system. To solve this problem, we analyze the use of hashing techniques that are available for obtaining retrieval. We specifically based on our analysis recommend the use of supervised hashing techniques over deep learned features as a possible common technique to solve this problem. Our investigation includes a comparison of some of the supervised and unsupervised methods viz. Principal Component Analysis (PCA), Locality Sensitive Hashing (LSH), Locality-sensitive binary codes from shift-invariant kernels (SKLSH), Iterative quantization: A procrustean approach to learning binary codes (ITQ), Binary Reconstructive Embedding (BRE) and Minimum loss hashing (MLH) that represent the prevalent classes of such systems and we present our analysis for the following biometric data: Face, Iris, and Fingerprint for a number of standard datasets. The main technical contributions through this work are as follows: (a) Proposing Siamese network based deep learned feature extraction method (b) Analysis of common feature extraction techniques for multiple biometrics as to a reduced feature space representation (c) Advocating the use of supervised hashing for obtaining a compact feature representation across different biometrics traits. (d) Analysis of the performance of deep representations against shallow representations in a practical reduced feature representation framework. Through experimentation with multiple biometrics traits, feature representations, and hashing techniques, we can conclude that current deep learned features when retrieved using supervised hashing can be a standard pipeline adopted for most unimodal and multimodal biometric identification tasks.</p

Electrically-driven phase transition in magnetite nanostructures

Magnetite (Fe$_{3}$O$_{4}$), an archetypal transition metal oxide, has been used for thousands of years, from lodestones in primitive compasses[1] to a candidate material for magnetoelectronic devices.[2] In 1939 Verwey[3] found that bulk magnetite undergoes a transition at T$_{V}$ $\approx$ 120 K from a high temperature "bad metal" conducting phase to a low-temperature insulating phase. He suggested[4] that high temperature conduction is via the fluctuating and correlated valences of the octahedral iron atoms, and that the transition is the onset of charge ordering upon cooling. The Verwey transition mechanism and the question of charge ordering remain highly controversial.[5-11] Here we show that magnetite nanocrystals and single-crystal thin films exhibit an electrically driven phase transition below the Verwey temperature. The signature of this transition is the onset of sharp conductance switching in high electric fields, hysteretic in voltage. We demonstrate that this transition is not due to local heating, but instead is due to the breakdown of the correlated insulating state when driven out of equilibrium by electrical bias. We anticipate that further studies of this newly observed transition and its low-temperature conducting phase will shed light on how charge ordering and vibrational degrees of freedom determine the ground state of this important compound.Comment: 17 pages, 4 figure

Radiation Effects in Ultraviolet Sensitive Pd/4H-SiC Schottky Detectors

9-154H-SiC, by virtue of its intrinsic properties, is a very promising semiconductor material for fabricating rad-hard UV detectors suitable for harsh radiation environments. This paper aims to investigate the radiation tolerance of indigenously developed Pd/4H-SiC Schottky detectors, in order to determine their feasibility for space applications. 4H-SiC detectors of active area 1 × 1 mm2 were irradiated with electrons of energy 10 MeV at fluence of 2×1013 e-/cm2 and gamma rays from a Co-60 source with a total dose of 1 Mrad. The impact of these irradiations on electro-optical characteristics of the devices was studied by analyzing the changes in electrical parameters like reverse saturation current (Is), ideality factor (n), barrier height (ɸB), effective doping concentration (Neff) derived from I-V and C-V characteristics as well as in the UV spectral responsivity (i.e., from 248 to 365 nm) of the irradiated detectors. The electron irradiated device showed negligible change in I-V and C-V characteristics whereas its UV spectral responsivity at the peak wavelength of 290 nm reduced by 48.7 %. Gamma irradiated device displayed a noticeable variation in its electrical characteristics and 15.8 % reduction in the spectral responsivity (optical characteristics) at the peak wavelength. The results show that the radiation hardness of 4H-SiC detectors is better than that of conventional semiconductor ones, making it a more appealing choice as radiation detectors in space systems

A checklist of ants of Thirunelli in Wayanad, Kerala

Volume: 107Start Page: 64End Page: 6

Radiation Effects in Ultraviolet Sensitive Pd/4H-SiC Schottky Detectors

4H-SiC, by virtue of its intrinsic properties, is a very promising semiconductor material for fabricating rad-hard UV detectors suitable for harsh radiation environments. This paper aims to investigate the radiation tolerance of indigenously developed Pd/4H-SiC Schottky detectors, in order to determine their feasibility for space applications. 4H-SiC detectors of active area 1 × 1 mm2 were irradiated with electrons of energy 10 MeV at fluence of 2×1013 e-/cm2 and gamma rays from a Co-60 source with a total dose of 1 Mrad. The impact of these irradiations on electro-optical characteristics of the devices was studied by analyzing the changes in electrical parameters like reverse saturation current (Is), ideality factor (n), barrier height (ɸB), effective doping concentration (Neff) derived from I-V and C-V characteristics as well as in the UV spectral responsivity (i.e., from 248 to 365 nm) of the irradiated detectors. The electron irradiated device showed negligible change in I-V and C-V characteristics whereas its UV spectral responsivity at the peak wavelength of 290 nm reduced by 48.7 %. Gamma irradiated device displayed a noticeable variation in its electrical characteristics and 15.8 % reduction in the spectral responsivity (optical characteristics) at the peak wavelength. The results show that the radiation hardness of 4H-SiC detectors is better than that of conventional semiconductor ones, making it a more appealing choice as radiation detectors in space systems