arXiv subjects

B. Lakshmi

Publications and source records attributed to B. Lakshmi.

4 recordsLinked to original sources

arXiv2011

Removing System Noise from Comparative Genomic Hybridization Data by Self-Self Analysis

Genomic copy number variation (CNV) is a large source of variation between organisms, and its consequences include phenotypic differences and genetic disorders. CNVs are commonly detected by hybridizing genomic DNA to microarrays of nucleic acid probes. System noise caused by operational and probe performance variability complicates the interpretation of these data. To minimize the distortion of genetic signal by system noise, we have explored the latter in an archive of hybridizations in which no genetic signal is expected. This archive is obtained by comparative genomic hybridization (CGH) of a sample in one channel to the same sample in the other channel, or 'self-self' data. These self-self hybridizations trap a variety of system noise inherent in sample-reference (test) data. Through singular value decomposition (SVD) of self-self data, we have determined the principal components of system noise. Assuming simple linear models of noise generation, the linear correction of test data with self-self data -or 'system normalization'- reduces local and long-range correlations and improves signal-to-noise metrics, yet does not introduce detectable spurious signal. Using this method, 90% of hybridizations displayed improved signal-to-noise ratios with an average increase of 7.0%, due mainly to a reduced median average deviation (MAD). In addition, we have found that principal component loadings correlate with specific probe variables including array coordinates, base composition, and proximity to the 5' ends of genes. The correlation of the principal component loadings with the test data depends on operational variables, such as the temporal order of processing and the localization of individual samples within 96-well plates.

q-bio.QM↗

arXiv2010

Statistical Modelling of ft to Process Parameters in 30 nm Gate Length Finfets

This paper investigates the effect of process variations on unity gain frequency (ft) in 30 nm gate length FinFET by performing extensive TCAD simulations. Six different geometrical parameters, channel doping, source/drain doping and gate electrode work function are studied for their sensitivity on ft. It is found that ft is more sensitive to gate length, underlap, gate-oxide thickness, channel and Source/Drain doping and less sensitive to source/drain width and length, and work function variations. Statistical modelling has been performed for ft through design of experiment with respect to sensitive parameters. The model has been validated through a comparison between random set of experimental data simulations and predicted values obtained from the model.

cs.OH↗

arXiv2004

Optical Spectroscopy of the Hole Spin in GaMnAs Acceptors

The spin state of holes bound to Mn acceptors in GaMnAs is investigated by optical spectroscopy. Concentrations of Mn from 10^17 to 10^19 cm^-3 were studied as a function of magnetic field and temperature. The photoluminescence from recombination of electrons with holes bound in the Mn-acceptor complex (MAC) displays multiple spectral peaks. The circular polarization rho of these peaks increases with increasing magnetic field and saturates at rho ~= 1/3. This value of polarization is expected from modeling the addition of spin angular momentum and interband optical transition matrix elements.

cond-mat.mtrl-sci↗

arXiv2003

Magnetic Interactions and Transport in (Ga,Cr)As

The magnetic, transport, and structural properties of (Ga,Cr)As are reported. Zincblende Ga$_{1-x}$Cr$_{x}$As was grown by low-temperature molecular beam epitaxy (MBE). At low concentrations, x$\sim$0.1, the materials exhibit unusual magnetic properties associated with the random magnetism of the alloy. At low temperatures the magnetization M(B) increases rapidly with increasing field due to the alignment of ferromagnetic units (polarons or clusters) having large dipole moments of order 10-10$^2$$μ_B$. A standard model of superparamagnetism is inadequate for describing both the field and temperature dependence of the magnetization M(B,T). In order to explain M(B) at low temperatures we employ a distributed magnetic moment (DMM) model in which polarons or clusters of ions have a distribution of moments. It is also found that the magnetic susceptibility increases for decreasing temperature but saturates below T=4 K. The inverse susceptibility follows a linear-T Curie-Weiss law and extrapolates to a magnetic transition temperature $θ$=10 K. In magnetotransport measurements, a room temperature resistivity of $ρ$=0.1 $Ω$cm and a hole concentration of $\sim10^{20}$ cm$^{-3}$ are found, indicating that Cr can also act as a acceptor similar to Mn. The resistivity increases rapidly for decreasing temperature below room temperature, and becomes strongly insulating at low temperatures. The conductivity follows exp[-(T$_1$/T)$^{1/2}$] over a large range of conductivity, possible evidence of tunneling between polarons or clusters.

cond-mat.mtrl-sci↗