A marked effect of water snails on small crustaceans. [Translation from: Anz.Ost.Akad.Wiss 10, 95-99, 1952. ]

Cases of mutual exclusion of two species of organisms in nature are known in large numbers. In the majority, they make different demands on the environ- ment which makes co-occurrence impossible. Less frequent are those cases in which a definite activity of one species prevents the occurrence of the other in the same region. An experiment was carried out n order to establish if Chydorus sphaericus can co-occur with water-snails. It emerged that a substance soluble in water which is given off by snails is responsible for the negative effect on small crustacea

Vibrational density of states of silicon nanoparticles

The vibrational density of states of silicon nanoparticles in the range from 2.3 to 10.3 nm is studied with the help of molecular-dynamics simulations. From these simulations the vibrational density of states and frequencies of bulk-like vibrational modes at high-symmetry points of the Brillouin-zone have been derived. The results show an increase of the density of states at low frequencies and a transfer of modes from the high-frequency end of the spectrum to the intermediate range. At the same time the peak of transverse optical modes is shifted to higher frequencies. These observations are in line with previous simulation studies of metallic nanoparticles and they provide an explanation for a previously observed discrepancy between experimental and theoretical data [C. Meier et al., Physica E, 32, 155 (2006)].Comment: 7 pages, 5 figure; accepted for publication in Phys. Rev.

A Novel Structure for Double Negative NIMs towards UV Spectrum with High FOM

A novel ring structure is proposed for double negative NIMs at visible light spectrum with high FOM (e.g. about 11 at a wavelength of 583 nm) and low loss. Besides the effective medium theory, an equivalent circuit model is also given to explain physically why our novel structure can give double negative behavior with low loss. Adapted from the original ring structure, two other types of structures, namely, disk and nanowire structures, are also given to further push double negative NIMs toward ultraviolet (UV) spectrum

An efficient way to reduce losses of left-handed metamaterials

We propose a simple and effective way to reduce the losses in left-handed metamaterials by manipulating the values of the effective parameters R, L, and C. We investigate the role of losses of the short-wire pairs and the fishnet structures. Increasing the effective inductance to capacitance ratio, L/C, reduces the losses and the figure of merit can increase substantially, especially at THz frequencies and in the optical regime

The Center of Excellence for Hypersonics Training and Research at the University of Texas at Austin

Over the period of this grant (1986-92), 23 graduate students were supported by the Center and received education and training in hypersonics through MS and Ph.D. programs. An additional 8 Ph.D. candidates and 2 MS candidates, with their own fellowship support, were attracted to The University of Texas and were recruited into the hypersonics program because of the Center. Their research, supervised by the 10 faculty involved in the Center, resulted in approximately 50 publications and presentations in journals and at national and international technical conferences. To provide broad-based training, a new hypersonics curriculum was created, enabling students to take 8 core classes in theoretical, computational, and experimental hypersonics, and other option classes over a two to four semester period. The Center also developed an active continuing education program. The Hypersonics Short Course was taught 3 times, twice in the USA and once in Europe. Approximately 300 persons were attracted to hear lectures by more than 25 of the leading experts in the field. In addition, a hypersonic aerodynamics short course was offered through AIAA, as well as short courses on computational fluid dynamics (CFD) and advanced CFD. The existence of the Center also enabled faculty to leverage a substantial volume of additional funds from other agencies, for research and graduate student training. Overall, this was a highly successful and highly visible program

Size Dependence and Convergence of the Retrieval Parameters of Metamaterials

We study the dependence of the retrieval parameters, such as the electric permittivity, the magnetic permeability and the index of refraction, $n$, on the size of the unit cell of a periodic metamaterial. The convergence of the retrieved parameters on the number of the unit cells is also examined. We have concentrated our studies on the so-called fishnet structure, which is the most promising design to obtain negative $n$ at optical wavelengths. We find that as the size of the unit cell decreases, the magnitude of the retrieved effective parameters increases. The convergence of the effective parameters of the fishnet as the number of the unit cells increases is demonstrated but found to be slower than for regular split ring resonators and wires structures. This is due to a much stronger coupling between the different unit cells in the fishnet structure.Comment: Journal-ref and DOI adde

An Automated Behavioral Analysis of Drosophila Melanogaster

Behavioral characteristics of D.melanogaster are strongly influenced by intrinsic and extrinsic factors, allowing scientists to assess how changes in physiology or environment manifest into behavior. Conversely, assessing changes in behavior of specimens provides valuable information about how the physiology of that organism responds to external changes. In this project, we developed a computer program to automate behavioral analyses of larvae and adult D. melanogaster aboard the International Space Station using on-board video recordings. Utilizing freely available libraries for Python, we set parameters to compute the number of animals, amount of locomotion as distance or movement, and the change in the perimeter of the larvae's outer shape to quantify behaviors such as curling or peristaltic full body wall contractions. Results show that our program is an efficient tool for analysis of larvae and adult locomotive behavior, thus providing scientists with a low-cost, efficient, and reliable method of quantifying behavioral data

Origin of Low Thermal Conductivity in Nuclear Fuels

Using a novel many-body approach, we report lattice dynamical properties of UO2 and PuO2 and uncover various contributions to their thermal conductivities. Via calculated Grueneisen constants, we show that only longitudinal acoustic modes having large phonon group velocities are efficient heat carriers. Despite the fact that some optical modes also show their velocities which are extremely large, they do not participate in the heat transfer due to their unusual anharmonicity. Ways to improve thermal conductivity in these materials are discussed.Comment: 4 pages, 3 figures, 1 tabl

Mechanical behavior of irregular fibers part III : the flexural buckling behavior

Fiber buckling behavior is associated with fabric-evoked prickle, which affects clothing comfort and aesthetics. In this paper, the flexural buckling behavior of irregular or nonuniform fibers is studied using the finite element method (FEM). Fiber dimensional irregularities are simulated with sine waves of different magnitude, frequency, and initial phase. The critical buckling loads of the simulated fibers are then calculated from the FE model. The results indicate that increasing the level of irregularity will decrease the critical buckling load of fibers, but the effect of the frequency and initial phase of irregularity on fiber buckling behavior is complicated and is affected by fiber diameter and effective length

Effective optical constants in stratified metal-dielectric metameterial

We present effective optical constants of stratified metal-dielectric metameterial. The effective constants are determined by two complex reflectivity method (TCRM). TCRM reveals full components of effective permittivity and permeability tensors and indicates the remarkable anisotropy of metallic and dielectric components below effective plasma frequency. On the other hand, above the plasma frequency, one of the effective refractive indexes takes a positive value less than unity and is associated with small loss. The photonic states are confirmed by the distribution of electromagnetic fields.Comment: 3 pages, 4 figures, to be published in Optics Letter