Correlating Threshold Power with Free-Space Bandwidth for Low-Directivity Antennas

This paper develops a threshold power rationale that can be used to demonstrate inherent compliance for portable wireless devices with specific absorption rate (SAR) limits over the 300-6000-MHz frequency range. This is achieved first by understanding the relationship between basic antenna parameters (bandwidth, operating frequency, and distance to the body) and SAR. From this, an upper limit is determined for the power transmitted by a portable wireless device such that the SAR will not exceed the compliance limit. Based on the presented computational and measured data, an empirical formula is developed for the threshold power as a function of the aforementioned parameters. It is demonstrated that the derived threshold power is conservative for all of the low-directivity antennas studied. Computed results are also compared against practical device data (mobile telephone data collected from the manufacturers) to show that the predicted threshold power data using the proposed formula are conservative. The limitations of the proposed formula are also discussed

Tests of the Accelerating Universe with Near-Infrared Observations of a High-Redshift Type Ia Supernova

We have measured the rest-frame B,V, and I-band light curves of a high-redshift type Ia supernova (SN Ia), SN 1999Q (z=0.46), using HST and ground-based near-infrared detectors. A goal of this study is the measurement of the color excess, E_{B-I}, which is a sensitive indicator of interstellar or intergalactic dust which could affect recent cosmological measurements from high-redshift SNe Ia. Our observations disfavor a 30% opacity of SN Ia visual light by dust as an alternative to an accelerating Universe. This statement applies to both Galactic-type dust (rejected at the 3.4 sigma confidence level) and greyer dust (grain size > 0.1 microns; rejected at the 2.3 to 2.6 sigma confidence level) as proposed by Aguirre (1999). The rest-frame $I$-band light cur ve shows the secondary maximum a month after B maximum typical of nearby SNe Ia of normal luminosi ty, providing no indication of evolution as a function of redshift out to z~0.5. A n expanded set of similar observations could improve the constraints on any contribution of extragalactic dust to the dimming of high-redshift SNe Ia.Comment: Accepted to the Astrophysical Journal, 12 pages, 2 figure

Ionization degree of the electron-hole plasma in semiconductor quantum wells

The degree of ionization of a nondegenerate two-dimensional electron-hole plasma is calculated using the modified law of mass action, which takes into account all bound and unbound states in a screened Coulomb potential. Application of the variable phase method to this potential allows us to treat scattering and bound states on the same footing. Inclusion of the scattering states leads to a strong deviation from the standard law of mass action. A qualitative difference between mid- and wide-gap semiconductors is demonstrated. For wide-gap semiconductors at room temperature, when the bare exciton binding energy is of the order of T, the equilibrium consists of an almost equal mixture of correlated electron-hole pairs and uncorrelated free carriers.Comment: 22 pages, 6 figure

Chandra ACIS Survey of M33 (ChASeM33): The enigmatic X-ray emission from IC131

We present the first X-ray analysis of the diffuse hot ionized gas and the point sources in IC131, after NGC604 the second most X-ray luminous giant HII region in M33. The X-ray emission is detected only in the south eastern part of IC131 (named IC131-se) and is limited to an elliptical region of ~200pc in extent. This region appears to be confined towards the west by a hemispherical shell of warm ionized gas and only fills about half that volume. Although the corresponding X-ray spectrum has 1215 counts, it cannot conclusively be told whether the extended X-ray emission is thermal, non-thermal, or a combination of both. A thermal plasma model of kT_e=4.3keV or a single power law of Gamma=2.1 fit the spectrum equally well. If the spectrum is purely thermal (non-thermal), the total unabsorbed X-ray luminosity in the 0.35-8keV energy band amounts to L_X = 6.8(8.7)x10^35erg/s. Among other known HII regions IC131-se seems to be extreme regarding the combination of its large extent of the X-ray plasma, the lack of massive O stars, its unusually high electron temperature (if thermal), and the large fraction of L_X emitted above 2keV (~40-53%). A thermal plasma of ~4keV poses serious challenges to theoretical models, as it is not clear how high electron temperatures can be produced in HII regions in view of mass-proportional and collisionless heating. If the gas is non-thermal or has non-thermal contributions, synchrotron emission would clearly dominate over inverse Compton emission. It is not clear if the same mechanisms which create non-thermal X-rays or accelerate CRs in SNRs can be applied to much larger scales of 200pc. In both cases the existing theoretical models for giant HII regions and superbubbles do not explain the hardness and extent of the X-ray emission in IC131-se.Comment: 28 pages, 7 figures and 2 tables. Accepted for publication in ApJ. For a high resolution version of the paper see http://hea-www.harvard.edu/vlp_m33_public/publications.htm

Multielectron effects in strong-field dissociative ionization of molecules

We study triple-ionization-induced, spatially asymmetric dissociation of N[subscript 2] using angular streaking in an elliptically polarized laser pulse in conjunction with few-cycle pump-probe experiments. The kinetic-energy-release dependent directional asymmetry in the ion sum-momentum distribution reflects the internuclear distance dependence of the fragmentation mechanism. Our results show that for 5–35-fs near-infrared laser pulses with intensities reaching 10[superscript 15] W/cm², charge exchange between nuclei plays a minor role in the triple ionization of N[subscript 2]. We demonstrate that angular streaking provides a powerful tool for probing multielectron effects in strong-field dissociative ionization of small molecules

Three-dimensional quantization of the electromagnetic field in dispersive and absorbing inhomogeneous dielectrics

A quantization scheme for the phenomenological Maxwell theory of the full electromagnetic field in an inhomogeneous three-dimensional, dispersive and absorbing dielectric medium is developed. The classical Maxwell equations with spatially varying and Kramers-Kronig consistent permittivity are regarded as operator-valued field equations, introducing additional current- and charge-density operator fields in order to take into account the noise associated with the dissipation in the medium. It is shown that the equal-time commutation relations between the fundamental electromagnetic fields $\hat E$ and $\hat B$ and the potentials $\hat A$ and $\hat \phi$ in the Coulomb gauge can be expressed in terms of the Green tensor of the classical problem. From the Green tensors for bulk material and an inhomogeneous medium consisting of two bulk dielectrics with a common planar interface it is explicitly proven that the well-known equal-time commutation relations of QED are preserved

Going Solo: Discovery of the First Parthenogenetic Gordiid (Nematomorpha: Gordiida)

Despite the severe fitness costs associated with sexual reproduction, its persistence and pervasiveness among multicellular organisms testifies to its intrinsic, short-term advantages. However, the reproductive assurance hypothesis predicts selection favoring asexual reproduction in sparse populations and when mate finding is difficult. Difficulties in finding mates is especially common in parasites, whose life cycles involve multiple hosts, or being released from the host into the external environment where the parasite can find itself trapped without a sexual partner. To solve this problem and guarantee reproduction, parasites in numerous phyla have evolved reproductive strategies, as predicted by the reproductive assurance hypothesis, such as hermaphroditism or parthenogenesis. However, this type of strategy has not been reported from species in the phylum Nematomorpha, whose populations have often been described as sparse. A new Nematomorpha species, Paragordius obamai n. sp., was discovered from Kenya, Africa, and appears to have solved the problem of being trapped without a mate by eliminating the need for males. Paragordius obamai n. sp. represents the first and only known species within this phylum to reproduce asexually. To determine the mechanism of this mating strategy, we ruled out the involvement of reproduction manipulating endosymbionts by use of next generation sequencing data, thus suggesting that parthenogenesis is determined genetically and may have evolved as a means to assure reproduction. Since this new parthenogenetic species and a closely related gonochoristic North American congener, P. varius, are easy to propagate in the laboratory, these gordiids can be used as model systems to test hypotheses on the genetic advantages and disadvantages of asexual reproduction and the genetic determinants of reproductive strategies in parasites