Linear electro-optic effects due to high order spatial dispersion

Two new types of electro-optic effect that are linear in the applied electric field strength are theoretically predicted to exist in transparent dielectric crystals due to high order spatial dispersion. The first effect, which is quadratic in the wave vector of light, is possible in materials belonging to all noncentrosymmetric crystal classes. The second, which is cubic in the wave vector, is possible in all crystals. In the ${\bm O}(432)$ and $\bm{O_h}(m\bar 3m)$ crystal classes, for which the primary and secondary linear electro-optic effects and linear electrogyration are simultaneously absent, these effects lead, respectively, to qualitatively new behavior and constitute the dominant bulk electro-optic effect in the limit of small fields. Thus, bulk linear electro-optic effects are predicted to exist in a wide range of materials---including many of considerable technological importance, such as silicon---where they were previously considered impossible.Comment: 10 pages, no figures, additional discussion included. Supplemental Material available from F. Castles on reques

A model for the Pockels effect in distorted liquid crystal blue phases

Recent experiments have found that a mechanically distorted blue phase can exhibit a primary linear electro-optic (Pockels) effect [F. Castles \textit{et al}. Nature Mater. \textbf{13}, 817 (2014)]. Here it is shown that flexoelectricity can account for the experimental results and a model, which is based on continuum theory but takes account of the sub-unit-cell structure, is proposed. The model provides a quantitative description of the effect accurate to the nearest order of magnitude and predicts that the Pockels coefficient(s) in an optimally-distorted blue phase may be two orders of magnitude larger than in lithium niobate.Comment: 11 pages, 2 figures. Supplemental Material available from F. Castles on reques

A sceptic looks at "housing theory"

A sceptic looks at "housing theory

Lower negative bounds on the static electric susceptibility of nonequilibrium cubic crystals

We use a classical, microscopic model of pointlike dipolarizable entities (a model that is standard in the case of positive polarizability) and investigate its behavior for simple cubic (sc), body-centered cubic (bcc), and face-centered cubic (fcc) crystals with one entity per primitive cell when the static polarizability of the entities is negative and the mutual electrostatic interaction between the entities is taken into account. We find that the static electric susceptibility is bounded below due to an instability towards self-polarization but negative values are possible in each case. The usual Clausius-Mossotti relation between the static polarizability and the static electric susceptibility remains valid in the case of negative parameters but is truncated at the lower bound; the value of the bound depends on the crystal structure and is always unrelated to the asymptote of the Clausius-Mossotti curve. The lower bounds of the static electric susceptibility are found to be -0.906 for sc and -1.00 for bcc and fcc. These results confirm that, although the magnitude of the static electric susceptibility does not diverge in the negative case (as it can in the positive case), the magnitudes attainable in the negative case for condensed media may, nevertheless, be many orders of magnitude greater than those predicted previously for inverted vapors and gases. This is a promising result in relation to the development of potential new technologies that exploit the phenomenon

Active Metamaterials with Negative Static Electric Susceptibility

Although well‐established textbook arguments suggest that static electric susceptibility χ(0) must be positive in “all bodies,” it has been pointed out that materials that are not in thermodynamic equilibrium are not necessarily subject to this restriction. Media with inverted populations of atomic and molecular energy levels have been predicted theoretically to exhibit a χ(0) < 0 state, however the systems envisioned require reduced temperature, reduced pressure, and an external pump laser to maintain the population inversion. Further, the existence of χ(0) < 0 has never been confirmed experimentally. Here, a completely different approach is taken to the question of χ(0) < 0 and a design concept to achieve “true” χ(0) < 0 is proposed based on active metamaterials with internal power sources. Two active metamaterial structures are fabricated that, despite still having their power sources implemented externally for reasons of practical convenience, provide evidence in support of the general concept. Effective values are readily achieved at room temperature and pressure and are tunable throughout the range of stability −1 < χ(0) < 0, resulting in experimentally‐determined magnitudes that are over one thousand times greater than those predicted previously. Since χ(0) < 0 is the missing electric analog of diamagnetism, this work opens the door to new technological capabilities such as stable electrostatic levitation

HI distribution and kinematics of NGC 1569

We present WSRT observations of high sensitivity and resolution of the neutral hydrogen in the starburst dwarf galaxy NGC 1569. Assuming a distance of 2.2 Mpc, we find a total HI mass of 1.3 * 10^8 M_sun to be distributed in the form of a dense, clumpy ridge surrounded by more extended diffuse HI containing a few additional discrete features, such as a Western HI Arm and an HI bridge reaching out to a small counterrotating companion cloud. About 10% by mass of all HI in NGC 1569 is at unusually high velocities. Some of this HI may be associated with the mass outflow evident from H-alpha measurements, but some may also be associated with NGC 1569's HI companion and intervening HI bridge, in which case, infall rather than outflow might be the cause of the discrepant velocities. No indication of a large bubble structure was found in position-velocity maps of the high-velocity HI. The galaxy as a whole is in modest overall rotation, but the HI gas lacks any sign of rotation within 60'' (0.6 kpc) from the center, i.e. over most of the optical galaxy. Here, turbulent motions resulting from the starburst appear to dominate over rotation. In the outer disk, the rotational velocities reach a maximum of 35 \pm 6 km/s, but turbulent motion remains significant. Thus, starburst effects are still noticeable in the outer HI disk, although they are no longer dominant beyond 0.6 kpc. Even excluding the most extreme high-velocity HI clouds, NGC 1569 still has an unusually high mean HI velocity dispersion of sigma_v=21.3 km/s, more than double that of other dwarf galaxies.Comment: Figure 11a,b and Figure 14 separately in jpg forma

A brief community linkage intervention for veterans with a persistent mental illness and a co-occurring substance abuse disorder

Objective: Individuals with co-occurring psychiatric and substance abuse problems often exhibit poor outpatient treatment engagement and re-hospitalization following discharge from acute psychiatric services. Although case management can improve treatment engagement and reduce attrition, these services are often delivered indefinitely, limiting the availability of treatment slots. In an effort to reduce re-hospitalization rates and improve outcomes during the transition from inpatient to outpatient treatment, we developed and evaluated Time-Limited Case Management (TLC), an eight-week integrated mental health and substance abuse augmentation intervention. Method: Sixty-five dually diagnosed veterans admitted to inpatient psychiatric treatment were included in the program evaluation, 32 who received the TLC service in addition to Treatment as Usual (TAU) that began during inpatient treatment and continued after the transition to outpatient services, and a comparison group of 33 who received only TAU without transitional support provided through the TLC augmentation service. Results: The TLC group had fewer days and episodes of hospitalization at two and six month post-study entry. Furthermore, the TLC group exhibited greater improvements on the Global Assessment of Functioning from baseline to the six-month follow-up. Conclusion: TLC appears to be an effective transitional augmentation service with benefits that persist beyond the eight weeks of the program. Future research should include a larger and more rigorously controlled trial to confirm the efficacy and unique contributions of the intervention