Automatic generation of hardware Tree Classifiers

Machine Learning is growing in popularity and spreading across different fields for various applications. Due to this trend, machine learning algorithms use different hardware platforms and are being experimented to obtain high test accuracy and throughput. FPGAs are well-suited hardware platform for machine learning because of its re-programmability and lower power consumption. Programming using FPGAs for machine learning algorithms requires substantial engineering time and effort compared to software implementation. We propose a software assisted design flow to program FPGA for machine learning algorithms using our hardware library. The hardware library is highly parameterized and it accommodates Tree Classifiers. As of now, our library consists of the components required to implement decision trees and random forests. The whole automation is wrapped around using a python script which takes you from the first step of having a dataset and design choices to the last step of having a hardware descriptive code for the trained machine learning model

Stellar mass functions of galaxies, disks and spheroids at z~0.1

We present the stellar mass functions (SMF) and mass densities of galaxies, and their spheroid and disk components in the local (z~0.1) universe over the range 8.9 <= log(M/M_solar) <= 12 from spheroid+disk decompositions and corresponding stellar masses of a sample of over 600,000 galaxies in the SDSS-DR7 spectroscopic sample. The galaxy SMF is well represented by a single Schechter function (M* = 11.116+/-0.011, alpha = -1.145+/-0.008), though with a hint of a steeper faint end slope. The corresponding stellar mass densities are (2.670+/-0.110), (1.687+/-0.063) and (0.910+/-0.029)x10^8 M_solar Mpc^-3 for galaxies, spheroids and disks respectively. We identify a crossover stellar mass of log(M/M_solar) = 10.3+/-0.030 at which the spheroid and disk SMFs are equal. Relative contributions of four distinct spheroid/disk dominated sub-populations to the overall galaxy SMF are also presented. The mean disk-to-spheroid stellar mass ratio shows a five fold disk dominance at the low mass end, decreasing monotonically with a corresponding increase in the spheroidal fraction till the two are equal at a galaxy stellar mass, log(M/M_solar)=10.479+/-0.013, the dominance of spheroids then grows with increasing stellar mass. The relative numbers of composite disk and spheroid dominated galaxies show peaks in their distributions, perhaps indicative of a preferred galaxy mass. Our characterization of the low redshift galaxy population provides stringent constraints for numerical simulations to reproduce.Comment: 30 pages, 18 figures, 5 tables (2 online), Accepted for publication in MNRA

Dark matter distribution in galaxy groups from combined strong lensing and dynamics analysis

Using a combined analysis of strong lensing and galaxy dynamics, we characterize the mass distributions and M/L ratios of galaxy groups, which form an important transition regime in Lambda-CDM cosmology. By mapping the underlying mass distribution, we test whether groups are dark matter dominated as hypothesized by the standard cosmogony, or isothermal as observed in baryon rich field galaxies. We present our lensing + galaxy dynamics formalism built around the dark matter dominant NFW and Hernquist distributions, compared against the Isothermal Sphere observed in galaxy scale objects. We show that mass measurement in the core of the group (r ~ 0.2 r_{vir}), determined jointly from a lens model and from differential velocity dispersion estimates, may effectively distinguish between these density distributions. We apply our method to MOS observations of two groups, SL2SJ1430+5546 and SL2SJ1431+5533, drawn from our CFHTLS lens catalog. With the measured lensing and dynamical masses, combined with a maximum likelihood estimator built around our model, we estimate the concentration index characterizing each density distribution and the corresponding virial mass of each group. Our results indicate that both groups are dark matter dominant, and reject the Isothermal distribution at >>3 sigma level. For both groups, the estimated i-band M/L ratios of ~260 Msun/Lsun, are similar to other published values for groups. The Gaussian distributions of the velocities of their member galaxies support a high degree of virialization. The differences in their virial masses, 2.8 and 1.6 x 10^14 Msun, and velocity dispersions, 720 and 560 km/s respectively, may indicate however that each group is at a different stage of transition to a cluster. We aim to populate this important transition regime with additional results from ongoing observations of the remaining lensing groups in our catalog.Comment: ApJ in press; 29 pages, including 10 figures and 7 tables. Latex with emulateapj v03/07/0

Ionized Nitrogen at High Redshift

We present secure [N II]_(205 μm) detections in two millimeter-bright, strongly lensed objects at high redshift, APM 08279+5255 (z = 3.911) and MM 18423+5938 (z = 3.930), using the IRAM Plateau de Bure Interferometer. Due to its ionization energy [N II]_(205 μm) is a good tracer of the ionized gas phase in the interstellar medium. The measured fluxes are S([N II]_(205 μm)) = (4.8 ± 0.8) Jy km s^(–1) and (7.4 ± 0.5) Jy km s^(–1), respectively, yielding line luminosities of L([N II]_(205 μm)) = (1.8 ± 0.3) × 10^9 μ^(–1) L_⊙ for APM 08279+5255 and L([N II]_(205 μm)) = (2.8 ± 0.2) × 10(^9) μ^(–1) L_⊙ for MM 18423+5938. Our high-resolution map of the [N II]_(205 μm) and 1 mm continuum emission in MM 18423+5938 clearly resolves an Einstein ring in this source and reveals a velocity gradient in the dynamics of the ionized gas. A comparison of these maps with high-resolution EVLA CO observations enables us to perform the first spatially resolved study of the dust continuum-to-molecular gas surface brightness (Σ_(FIR)α Σ^N_CO, which can be interpreted as the star formation law) in a high-redshift object. We find a steep relation (N = 1.4 ± 0.2), consistent with a starbursting environment. We measure a [N II]_(205 μm)/FIR luminosity ratio in APM 08279+5255 and MM 18423+5938 of 9.0 × 10^(–6) and 5.8 × 10^(–6), respectively. This is in agreement with the decrease of the [N II]_(205 μm)/FIR ratio at high FIR luminosities observed in local galaxies

Group-finding with photometric redshifts: The Photo-z Probability Peaks algorithm

We present a galaxy group-finding algorithm, the Photo-z Probability Peaks (P3) algorithm, optimized for locating small galaxy groups using photometric redshift data by searching for peaks in the signal-to-noise of the local overdensity of galaxies in a three-dimensional grid. This method is an improvement over similar two-dimensional matched-filter methods in reducing background contamination through the use of redshift information, allowing it to accurately detect groups at lower richness. We present the results of tests of our algorithm on galaxy catalogues from the Millennium Simulation. Using a minimum S/N of 3 for detected groups, a group aperture size of 0.25 Mpc/h, and assuming photometric redshift accuracy of sigma_z = 0.05 it attains a purity of 84% and detects ~295 groups/deg.^2 with an average group richness of 8.6 members. Assuming photometric redshift accuracy of sigma_z = 0.02, it attains a purity of 97% and detects ~143 groups/deg.^2 with an average group richness of 12.5 members. We also test our algorithm on data available for the COSMOS field and the presently-available fields from the CFHTLS-Wide survey, presenting preliminary results of this analysis.Comment: Accepted for publication by MNRAS, 16 pages, 11 color figure

What shapes a galaxy? - Unraveling the role of mass, environment and star formation in forming galactic structure

We investigate the dependence of galaxy structure on a variety of galactic and environmental parameters for ~500,000 galaxies at z<0.2, taken from the Sloan Digital Sky Survey data release 7 (SDSS-DR7). We utilise bulge-to-total stellar mass ratio, (B/T)_*, as the primary indicator of galactic structure, which circumvents issues of morphological dependence on waveband. We rank galaxy and environmental parameters in terms of how predictive they are of galaxy structure, using an artificial neural network approach. We find that distance from the star forming main sequence (Delta_SFR), followed by stellar mass (M_*), are the most closely connected parameters to (B/T)_*, and are significantly more predictive of galaxy structure than global star formation rate (SFR), or any environmental metric considered (for both central and satellite galaxies). Additionally, we make a detailed comparison to the Illustris hydrodynamical simulation and the LGalaxies semi-analytic model. In both simulations, we find a significant lack of bulge-dominated galaxies at a fixed stellar mass, compared to the SDSS. This result highlights a potentially serious problem in contemporary models of galaxy evolution.Comment: Accepted to MNRAS. 31 pages, 15 figure

ELECTROKINETIC INSTABILITIES IN FERROFLUID MICROFLOWS

Lab-on-a-chip devices have been increasingly used in the past two decades for chemical and biomedical analysis. These devices employ the concepts of microfluidics and offer the promise of incorporating multiple laboratory processes onto a single portable chip. Electric field has been often employed in microfluidic devices for the ease of fluid and sample control as well as the convenience of chip integration and interfacing. Flow instabilities can take place when two fluids of unequal electrical properties are pumped through a microchannel under the application of an adequately strong electric field. The study of these electrokinetic instabilities in microfluidic devices is not only significant to fundamental research but also relevant to practical applications such as sample mixing. In this work an experimental investigation of the electrokinetic instability between co-flowing ferrofluid and DI water in a T-shaped microchannel is carried out. The effects of the applied DC electric field and the ferrofluid concentration on the flow pattern are examined. For each concentration of ferrofluid, pure diffusion happens until a certain value of electric field, above which instability waves are generated at the interface of the ferrofluid and DI-water flows and convected downstream. Moreover, these waves become more irregular and even chaotic with the increase in electric field. This threshold electric field is found to decrease with the increase in ferrofluid concentration. Meanwhile, a two-dimensional transient numerical model using commercial solver COMSOL 4.3b is also developed to simulate the electrokinetic instability phenomenon by employing the electrical conductivity difference between DI water and ferrofluid. Theoretical analysis of the equations governing electrokinetic flows show that free charges are generated in a fluid with conductivity gradients in the presence of electric field. The action of electric field on these free charges result in Coulomb force that generates instability when strong enough. The effect of electric field on the flow is simulated and the threshold electric field is found through a series of simulations for each ferrofluid concentration. The simulation result trend is in good agreement with the experiments, but the numerical model under predicts the threshold electric field found through experiments. Furthermore, the effect of permittivity variation between ferrofluid and DI-water is included in the numerical model to understand its influence on the electrokinetic instability pattern and threshold electric field. Theoretical analysis shows that the presence of permittivity gradient can also induce an electrical force in the bulk fluid in the presence of electric field. This force is opposite to that generated by the conductivity gradient, and hence serves to stabilize the flow, which should lift the threshold electric field for electrokinetic instability. Such an influence is, however, found to be insignificant through the numerical model accounting for both conductivity and permittivity gradients. The numerical model assumes ferrofluid as a continuous fluid and hence the electrophoretic and magnetophoretic forces experienced by the nanoparticles are not incorporated. A brief study about the effects of these factors on the threshold electric field indicates their insignificant influence. The possible deviation in the diffusion coefficient of ferrofluid is also investigated in the numerical model, whose influence is also found to be inconsequential. It is supposed that the top and bottom wall effects on the electrokinetic instability should be taken into consideration by the use of a three-dimensional numerical model