Elastomeric microfluidic diode and rectifier work with Newtonian fluids

We report on two microfluidic elastomeric autoregulatory devices—a diode and a rectifier. They exhibit physically interesting and complex nonlinear behaviors (saturation, bias-dependent resistance, and rectification) with a Newtonian fluid. Due to their autoregulatory properties, they operate without active external control. As a result, they enable increased microfluidic device density and overall system miniaturization. The demonstrated diode and rectifier would also be useful components in future microfluidic logic circuitry

Redshift-space distortions around voids

We have derived estimators for the linear growth rate of density fluctuations using the cross-correlation function of voids and haloes in redshift space, both directly and in Fourier form. In linear theory, this cross-correlation contains only monopole and quadrupole terms. At scales greater than the void radius, linear theory is a good match to voids traced out by haloes in N-body simulations; small-scale random velocities are unimportant at these radii, only tending to cause small and often negligible elongation of the redshift-space cross-correlation function near its origin. By extracting the monopole and quadrupole from the cross-correlation function, we measure the linear growth rate without prior knowledge of the void profile or velocity dispersion. We recover the linear growth parameter $\beta$ to 9% precision from an effective volume of 3(Gpc/h)^3 using voids with radius greater than 25Mpc/h. Smaller voids are predominantly sub-voids, which may be more sensitive to the random velocity dispersion; they introduce noise and do not help to improve the measurement. Adding velocity dispersion as a free parameter allows us to use information at radii as small as half of the void radius. The precision on $\beta$ is reduced to approximately 5%. Contrary to the simple redshift-space distortion pattern in overdensities, voids show diverse shapes in redshift space, and can appear either elongated or flattened along the line of sight. This can be explained by the competing amplitudes of the local density contrast, plus the radial velocity profile and its gradient, with the latter two factors being determined by the cumulative density profile of voids. The distortion pattern is therefore determined solely by the void profile and is different for void-in-cloud and void-in-void. This diversity of redshift-space void morphology complicates measurements of the Alcock-Paczynski effect using voids.Comment: 14 pages, 6 figures, minor changes to match the published version in MNRA

Measurement and models accounting for cell death capture hidden variation in compound response.

Cancer cell sensitivity or resistance is almost universally quantified through a direct or surrogate measure of cell number. However, compound responses can occur through many distinct phenotypic outcomes, including changes in cell growth, apoptosis, and non-apoptotic cell death. These outcomes have divergent effects on the tumor microenvironment, immune response, and resistance mechanisms. Here, we show that quantifying cell viability alone is insufficient to distinguish between these compound responses. Using an alternative assay and drug-response analysis amenable to high-throughput measurement, we find that compounds with identical viability outcomes can have very different effects on cell growth and death. Moreover, additive compound pairs with distinct growth/death effects can appear synergistic when only assessed by viability. Overall, these results demonstrate an approach to incorporating measurements of cell death when characterizing a pharmacologic response

Using ultrashort optical pulses to couple ferroelectric and ferromagnetic order in an oxide heterostructure

A new approach to all-optical detection and control of the coupling between electric and magnetic order on ultrafast timescales is achieved using time-resolved second harmonic generation (SHG) to study a ferroelectric (FE)/ferromagnet (FM) oxide heterostructure. We use femtosecond optical pulses to modify the spin alignment in a Ba$_{0.1}$Sr$_{0.9}$TiO$_{3}$(BSTO)/La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ (LCMO) heterostructure and selectively probe the ferroelectric response using SHG. In this heterostructure, the pump pulses photoexcite non-equilibrium quasiparticles in LCMO, which rapidly interact with phonons before undergoing spin-lattice relaxation on a timescale of tens of picoseconds. This reduces the spin-spin interactions in LCMO, applying stress on BSTO through magnetostriction. This then modifies the FE polarization through the piezoelectric effect, on a timescale much faster than laser-induced heat diffusion from LCMO to BSTO. We have thus demonstrated an ultrafast indirect magnetoelectric effect in a FE/FM heterostructure mediated through elastic coupling, with a timescale primarily governed by spin-lattice relaxation in the FM layer

A microfluidic processor for gene expression profiling of single human embryonic stem cells

The gene expression of human embryonic stem cells (hESC) is a critical aspect for understanding the normal and pathological development of human cells and tissues. Current bulk gene expression assays rely on RNA extracted from cell and tissue samples with various degree of cellular heterogeneity. These cell population averaging data are difficult to interpret, especially for the purpose of understanding the regulatory relationship of genes in the earliest phases of development and differentiation of individual cells. Here, we report a microfluidic approach that can extract total mRNA from individual single-cells and synthesize cDNA on the same device with high mRNA-to-cDNA efficiency. This feature makes large-scale single-cell gene expression profiling possible. Using this microfluidic device, we measured the absolute numbers of mRNA molecules of three genes (B2M, Nodal and Fzd4) in a single hESC. Our results indicate that gene expression data measured from cDNA of a cell population is not a good representation of the expression levels in individual single cells. Within the G0/G1 phase pluripotent hESC population, some individual cells did not express all of the 3 interrogated genes in detectable levels. Consequently, the relative expression levels, which are broadly used in gene expression studies, are very different between measurements from population cDNA and single-cell cDNA. The results underscore the importance of discrete single-cell analysis, and the advantages of a microfluidic approach in stem cell gene expression studies

Variational calculations on the hydrogen molecular ion

We present high-precision non-relativistic variational calculations of bound vibrational-rotational state energies for the $H_2^+$ and $D_2^+$ molecular ions in each of the lowest electronic states of $\Sigma_g$, $\Sigma_u$, and $\Pi_u$ symmetry. The calculations are carried out including coupling between $\Sigma$ and $\Pi$ states but without using the Born-Oppenheimer or any adiabatic approximation. Convergence studies are presented which indicate that the resulting energies for low-lying levels are accurate to about $10^{-13}$. Our procedure accounts naturally for the lambda-doubling of the $\Pi_u$ state.Comment: 23 pp., RevTeX, epsf.sty, 5 figs. Enhanced data in Table II, dropped 3 figs. from previous versio

Size evolution of the most massive galaxies at 1.7<z<3 from GOODS NICMOS survey imaging

We measure the sizes of 82 massive (M>10^11 M_sun) galaxies at 1.7<z<3 utilizing deep HST NICMOS data taken in the GOODS North and South fields. Our sample is almost an order of magnitude larger than previous studies at these redshifts, providing the first statistical study of massive galaxy sizes at z>2, confirming the extreme compactness of these galaxies. We split our sample into disk-like (n2) galaxies based on their Sersic indices, and find that at a given stellar mass disk-like galaxies at z~2.3 are a factor of 2.6+/-0.3 smaller than present day equal mass systems, and spheroid-like galaxies at the same redshifts are 4.3+/-0.7 smaller than comparatively massive elliptical galaxies today. At z>2 our results are compatible with both a leveling off, or a mild evolution in size. Furthermore, the high density (~2x10^10 M_sun kpc^-3) of massive galaxies at these redshifts, which are similar to present day globular clusters, possibly makes any further evolution in sizes beyond z=3 unlikely.Comment: 5 pages, 2 figures, 2 tables, accepted by ApJ Letters, minor changes added to match the accepted versio

Polaronic transport induced by competing interfacial magnetic order in a La0.7_{0.7}Ca0.3_{0.3}MnO3_{3}/BiFeO3_{3} heterostructure

Using ultrafast optical spectroscopy, we show that polaronic behavior associated with interfacial antiferromagnetic order is likely the origin of tunable magnetotransport upon switching the ferroelectric polarity in a La$_{0.7}$Ca$_{0.3}$MnO$_{3}$/BiFeO$_{3}$ (LCMO/BFO) heterostructure. This is revealed through the difference in dynamic spectral weight transfer between LCMO and LCMO/BFO at low temperatures, which indicates that transport in LCMO/BFO is polaronic in nature. This polaronic feature in LCMO/BFO decreases in relatively high magnetic fields due to the increased spin alignment, while no discernible change is found in the LCMO film at low temperatures. These results thus shed new light on the intrinsic mechanisms governing magnetoelectric coupling in this heterostructure, potentially offering a new route to enhancing multiferroic functionality