Postcopulatory sexual selection

The female reproductive tract is where competition between the sperm of different males takes place, aided and abetted by the female herself. Intense postcopulatory sexual selection fosters inter-sexual conflict and drives rapid evolutionary change to generate a startling diversity of morphological, behavioural and physiological adaptations. We identify three main issues that should be resolved to advance our understanding of postcopulatory sexual selection. We need to determine the genetic basis of different male fertility traits and female traits that mediate sperm selection; identify the genes or genomic regions that control these traits; and establish the coevolutionary trajectory of sexes

Evolution of sex-specific pace-of-life syndromes: genetic architecture and physiological mechanisms

Sex differences in life history, physiology, and behavior are nearly ubiquitous across taxa, owing to sex-specific selection that arises from different reproductive strategies of the sexes. The pace-of-life syndrome (POLS) hypothesis predicts that most variation in such traits among individuals, populations, and species falls along a slow-fast pace-of-life continuum. As a result of their different reproductive roles and environment, the sexes also commonly differ in pace-of-life, with important consequences for the evolution of POLS. Here, we outline mechanisms for how males and females can evolve differences in POLS traits and in how such traits can covary differently despite constraints resulting from a shared genome. We review the current knowledge of the genetic basis of POLS traits and suggest candidate genes and pathways for future studies. Pleiotropic effects may govern many of the genetic correlations, but little is still known about the mechanisms involved in trade-offs between current and future reproduction and their integration with behavioral variation. We highlight the importance of metabolic and hormonal pathways in mediating sex differences in POLS traits; however, there is still a shortage of studies that test for sex specificity in molecular effects and their evolutionary causes. Considering whether and how sexual dimorphism evolves in POLS traits provides a more holistic framework to understand how behavioral variation is integrated with life histories and physiology, and we call for studies that focus on examining the sex-specific genetic architecture of this integration

Synchrotron diffraction studies of lead octadecanoate, tetracosanoic acid and 1-eicosanol monolayers on water

We have used diffraction of synchrotron radiation to study Langmuir monolayers of several different materials. Lead octadecanoate (stearate) was seen to undergo first order melting, although there is no clear indication of this in its isotherm. 1-eicosanol, which has a "kink" in its isotherm, shows diffraction peaks of similar size both above and below this kink. Tetracosanoic acid shows, at high pressure, a second peak close to the first. © 1988.link_to_subscribed_fulltex

Excitonic gain and stimulated ultraviolet emission in nanocrystalline zinc-oxide powder

We have studied ultraviolet photoluminescence from high-purity zinc-oxide powder over a wide temperature range (2-293 K). At low temperatures, the spontaneous emission is due to radiative recombination of excitons bound to donors and acceptors. At high temperature (> 90 K), it mainly consists of recombination of free excitons, with exciton-exciton collision-induced recombination dominating the spectrum at higher pumping intensities. Emission from the exciton-exciton collision process shows clear stimulated-emission behavior. At sufficiently high pumping intensity, the stimulated emission band shifts abruptly to a longer wavelength due to the formation of an electron-hole plasma. Sharp emission peaks are observed in the stimulated emission bands. The possible origins of these sharp peaks are discussed. (C) 2000 American Institute of Physics. [S0003-6951(00)01341-3]

Optical second-harmonic generation in sputter-deposited AlN films

Results of a study of optical second-harmonic (SH) generation in AlN films deposited on borosilicate glass by reactive direct current magnetron sputtering are reported. As determined by x-ray diffraction (XRD), the films were highly c-axis oriented. The transmitted SH signal for film thickness ranging from 340 to 7800 Angstrom was measured. The signal was consistent with the existence of a dead layer (in which no SH was generated) on the film surface with an effective thickness of 300 Angstrom. A set of 7800-Angstrom-thick films were deposited at substrate temperatures from ambient to T-s = 400 degrees C. For films deposited at 100 degrees C or higher, minimal variation in the SH signal with T-s was found. Values of \textbackslash{}d(33)\textbackslash{} = 4 pm/V and \textbackslash{}d(31)\textbackslash{} = 0.04 pm/V, with d(33) and d(31) having the same sign, were obtained for T-s = 400 degrees C. The approximate tilt angle of the optic axis of the films with respect to the substrate surface normal was determined. XRD results showed that the tilt was due to a tilt of the crystallographic texture axis. (C) 1998 American Institute of Physics. [S0021-8979(98)09423-7

Apparatus for making A/B superlattice Langmuir-Blodgett films

We report a modification recently made to a Langmuir-Blodgett superlattice apparatus previously described in this journal. The modification permits the preparation of so-called A/B superlattices consisting of the sequence ABAB⋯, where A and B are monolayers of two different film-forming molecules deposited into a multilayer structure.link_to_subscribed_fulltex

Kinetics of a structural phase transition in Langmuir monolayers studied using x-ray diffraction

Frequently, time-dependent effects are seen in monolayers of amphiphilic molecules (Langmuir films) when they are compressed, so that the pressure after some time is different from that recorded immediately after compression. We have identified for the first time a microscopic relaxation mechanism in monolayers of heneicosanol (C21,H43OH): namely, a transition from a uniaxially distorted ("pseudohexagonal") structure, formed upon compression, to an undistorted hexagonal structure. For T > 20°C we observe only an apparently hexagonal phase, while at T = 5°C we observe only an apparently stable pseudohexagonal phase. When 10≤T≤20°C, the monolayer structure changes with time from pseudohexagonal to hexagonal. The rate at which this transformation occurs is strongly temperature dependent. We propose that the observed temperature dependence is determined by the rate of nucleation of a hexagonal phase from a metastable shear-induced structure. © 1989 American Institute of Physics.link_to_subscribed_fulltex

X-ray diffraction studies of organic monolayers on the surface of water

We have used synchrotron radiation to study organic monolayers on water ("Langmuir films"). At high monolayer pressures, lead stearate [Pb(C17H35COO)2] shows a powder peak at 1.60 -1, implying an area per unit cell of 17.8 2 if the lattice is triangular. The correlation length is about 250. Lignoceric acid (C23H47COOH) shows a similar peak even though no heavy ions are attached. When the pressure is reduced, the peak in lead stearate does not observably move or broaden; below the "knee" in the isotherm, however, the peak height decreases slowly with increasing area, implying a first-order melting transition. © 1987 The American Physical Society.link_to_subscribed_fulltex

Kinetics of a structural phase transition in Langmuir monolayers studied using x-ray diffraction

Frequently, time-dependent effects are seen in monolayers of amphiphilic molecules (Langmuir films) when they are compressed, so that the pressure after some time is different from that recorded immediately after compression. We have identified for the first time a microscopic relaxation mechanism in monolayers of heneicosanol (C21,H43OH): namely, a transition from a uniaxially distorted ("pseudohexagonal") structure, formed upon compression, to an undistorted hexagonal structure. For T > 20°C we observe only an apparently hexagonal phase, while at T = 5°C we observe only an apparently stable pseudohexagonal phase. When 10≤T≤20°C, the monolayer structure changes with time from pseudohexagonal to hexagonal. The rate at which this transformation occurs is strongly temperature dependent. We propose that the observed temperature dependence is determined by the rate of nucleation of a hexagonal phase from a metastable shear-induced structure. © 1989 American Institute of Physics.link_to_subscribed_fulltex

Thermoelectric transport properties of n-doped and p-doped Bi0.91Sb0.09 alloy thin films

In order to understand the doping behavior of extremely narrow band gap materials and to optimize their characteristics for use in a thermoelectric module, we performed n- and p- type doping experiments on semiconducting Bi0.91Sb0.09 alloy thin films using the group VI(IV) element Te(Sn) as donor (acceptor). Thermoelectric power (TEP), electrical resistivity, and Hall effect were studied in the range of temperatures 5-300 K. Increased Sn doping causes the TEP to change sign (from negative to positive) and the maximum in the TEP can be controlled with the dopant concentration. Increased Te doping causes the TEP to decrease. The maximum Te- oped electron concentration was about 5x10(20) cm(-3) and the highest Sn-doped hole concentration was about 1x10(21) cm(-3). Highly Sn- and Te-doped samples show degenerate behavior in the electrical resistivity, TEP and Hall measurements. (C) 1999 American Institute of Physics. [S0021-8979(99)02707-3]