Multi-directional sorting modes in deterministic lateral displacement devices

Deterministic lateral displacement (DLD) devices separate micrometer-scale particles in solution based on their size using a laminar microfluidic flow in an array of obstacles. We investigate array geometries with rational row-shift fractions in DLD devices by use of a simple model including both advection and diffusion. Our model predicts novel multi-directional sorting modes that could be experimentally tested in high-throughput DLD devices containing obstacles that are much smaller than the separation between obstacles

Measurements of thermodynamic and transport properties of EuC2_2: a low-temperature analogue of EuO

EuC$_2$ is a ferromagnet with a Curie-temperature of $T_C \simeq 15\,$K. It is semiconducting with the particularity that the resistivity drops by about 5 orders of magnitude on cooling through $T_C$, which is therefore called a metal-insulator transition. In this paper we study the magnetization, specific heat, thermal expansion, and the resistivity around this ferromagnetic transition on high-quality EuC$_2$ samples. At $T_C$ we observe well defined anomalies in the specific heat $c_p(T)$ and thermal expansion $\alpha(T)$ data. The magnetic contributions of $c_p(T)$ and $\alpha(T)$ can satisfactorily be described within a mean-field theory, taking into account the magnetization data. In zero magnetic field the magnetic contributions of the specific heat and thermal expansion fulfill a Gr\"uneisen-scaling, which is not preserved in finite fields. From an estimation of the pressure dependence of $T_C$ via Ehrenfest's relation, we expect a considerable increase of $T_C$ under applied pressure due to a strong spin-lattice coupling. Furthermore the influence of weak off stoichiometries $\delta$ in EuC$_{2 \pm \delta}$ was studied. It is found that $\delta$ strongly affects the resistivity, but hardly changes the transition temperature. In all these aspects, the behavior of EuC$_2$ strongly resembles that of EuO.Comment: 7 pages, 6 figure

The twist angle has weak influence on charge separation and strong influence on recombination in the MoS₂/WS₂ bilayer: ab initio quantum dynamics

Van der Waals heterojunctions of two-dimensional transition-metal dichalcogenides are intensely investigated for multiple optoelectronics applications. Strong and adjustable interactions between layers can influence the charge and energy flow that govern material performance. We report ab initio quantum molecular dynamics investigation of the influence of the bilayer twist angle on charge transfer and recombination in MoS2/WS2 heterojunctions, including high-symmetry 0° and 60° configurations, and low symmetry 9.43° and 50.57° structures with Moiré patterns. The twist angle modulates interlayer coupling, as evidenced by changes in the interlayer distance, electron-vibrational interactions, and spectral shifts in the out-of-plane vibrational frequencies. Occurring on a femtosecond timescale, the hole transfer depends weakly on the twist angle and is ultrafast due to high density of acceptor states and large nonadiabatic coupling. In contrast, the electron–hole recombination takes nanoseconds and varies by an order of magnitude depending on the twist angle. The recombination is slow because it occurs across a large energy gap. It depends on the twist angle because the nonadiabatic coupling is sensitive to the interlayer distance and overlap of electron and hole wavefunctions. The Moiré pattern systems exhibit weaker interlayer interaction, generating longer-lived charges. Both charge separation and recombination are driven by out-of-plane vibrational motions. The simulations rationalize the experimental results on the influence of the bilayer twist angle on the charge separation and recombination. The atomistic insights provide theoretical guidance for design of high-performance optoelectronic devices based on 2D van der Waals heterostructures

Factor demand linkages, technology shocks, and the business cycle

This paper argues that factor demand linkages can be important for the transmission of both sectoral and aggregate shocks. We show this using a panel of highly disaggregated manufacturing sectors together with sectoral structural VARs. When sectoral interactions are explicitly accounted for, a contemporaneous technology shock to all manufacturing sectors implies a positive response in both output and hours at the aggregate level. Otherwise there is a negative correlation, as in much of the existing literature. Furthermore, we find that technology shocks are important drivers of the business cycle

Density Matrix in Quantum Mechanics and Distinctness of Ensembles Having the Same Compressed Density Matrix

We clarify different definitions of the density matrix by proposing the use of different names, the full density matrix for a single-closed quantum system, the compressed density matrix for the averaged single molecule state from an ensemble of molecules, and the reduced density matrix for a part of an entangled quantum system, respectively. We show that ensembles with the same compressed density matrix can be physically distinguished by observing fluctuations of various observables. This is in contrast to a general belief that ensembles with the same compressed density matrix are identical. Explicit expression for the fluctuation of an observable in a specified ensemble is given. We have discussed the nature of nuclear magnetic resonance quantum computing. We show that the conclusion that there is no quantum entanglement in the current nuclear magnetic resonance quantum computing experiment is based on the unjustified belief that ensembles having the same compressed density matrix are identical physically. Related issues in quantum communication are also discussed.Comment: 26 pages. To appear in Foundations of Physics, 36 (8), 200

On Forward J/\psi Production at Fermilab Tevatron

The D0 Collaboration has recently reported the measurement of J/\psi production at low angle. We show here that the inclusion of color octet contributions in any framework is able to reproduce this data.Comment: 1 page, Revtex, uses epsfig.sty, 2 postscript figure

Soft Color Enhancement of the Production of J/psi's by Neutrinos

We calculate the production of J/psi mesons by neutrino-nucleon collisions in fixed target experiments. Soft color, often referred to as color evaporation effects, enhance production cross sections due to the contribution of color octet states. Though still small, J/\psi production may be observable in present and future experiments like NuTeV and muon colliders.Comment: 7 pages, Revtex, 4 postscript figures, uses epsfig.st

HST/FOS Eclipse Observations of the Nova-like Cataclysmic Variable UX Ursae Majoris

[abridged abstract] We present and analyze Hubble Space Telescope observations of the eclipsing nova-like cataclysmic variable UX UMa obtained with the Faint Object Spectrograph. Two eclipses each were observed with the G160L grating (covering the ultraviolet waveband) in August of 1994 and with the PRISM (covering the near-ultraviolet to near-infrared) in November of the same year. The system was 50% brighter in November than in August, which, if due to a change in the accretion rate, indicates a fairly substantial increase in Mdot_acc by >~ 50%. Model disk spectra constructed as ensembles of stellar atmospheres provide poor descriptions of the observed post-eclipse spectra, despite the fact that UX UMa's light should be dominated by the disk at this time. Suitably scaled single temperature model stellar atmospheres with T_eff = 12,500-14,500 K actually provide a better match to both the ultraviolet and optical post-eclipse spectra. Evidently, great care must be taken in attempts to derive accretion rates from comparisons of disk models to observations. One way to reconcile disk models with the observed post-eclipse spectra is to postulate the presence of a significant amount of optically thin material in the system. Such an optically thin component might be associated with the transition region (``chromosphere'') between the disk photosphere and the fast wind from the system, whose presence has been suggested by Knigge & Drew (1997).Comment: 35 pages, including 12 figures; to appear in the ApJ (Vol. 499