Achromatic optical phase shifter/modulator

We propose and demonstrate, theoretically and experimentally, a novel achromatic optical phase shifter modulator based on a frequency-domain optical delay line configured to maintain zero group delay as variable phase delay is generated by means of tilting a mirror. Compared with previously reported phase shifter modulators, e.g., based on the Pancharatnam (geometric) phase, our device is high speed and polarization insensitive and produces a large, bounded phase delay that, uniquely, is one-to-one mapped to a measurable parameter, the tilt angle.

Bidirectional incompatibility between conspecific populations of Drosophila simulans

Cytoplasmic incompatibility (CI) describes the phenomenon whereby eggs fertilized by sperm from insects infected with a rickettsial endosymbiont fail to hatch. Unidirectional CI between conspecific populations of insects is a well documented phenomenon. Bidirectional CI has, however, only been described in mosquito populations, and recently between closely related species of parasitic wasps, where it is of interest as both an unusual form of reproductive isolation and as a potential means of insect population suppression. Here we report on the first known example of bidirectional CI between conspecific populations of Drosophila simulans. Further, we show that defects as early as the first cleavage division are associated with CI. This observation suggests that the cellular basis of CI involves disruption of processes before or during zygote formation and that CI arises from defects in the structure and/or function of the sperm during fertilization.

Review of Contact and Dynamic Phenomena in Cold Roll Forming

This review reflects the state of the art in study of contact and dynamic phenomena occurring in cold roll forming. The importance of taking these phenomena into account is determined by significant machine time and tooling costs spent on worn out forming rolls replacement and equipment adjustment in cold roll forming. Predictive modelling of the tool wear caused by contact and dynamic phenomena can reduce the production losses in this technological process.

Anodic-oxide-induced interdiffusion in GaAs/AlGaAs quantum wells

Enhancement of interdiffusion in GaAs/AlGaAs quantum wells due to anodic oxides was studied. Photoluminescence, transmission electron microscopy, and quantum well modeling were used to understand the effects of intermixing on the quantum well shape. Residual water in the oxide was found to increase the intermixing, though it was not the prime cause for intermixing. Injection of defects such as group III vacancies or interstitials was considered to be a driving force for the intermixing. Different current densities used in the experimental range to create anodic oxides had little effect on the intermixing. ©1998 American Institute of Physics.

Annealing of ion implanted gallium nitride

In this paper, we examine Si and Te ion implant damage removal in GaN as a function of implantation dose, and implantation and annealing temperature. Transmission electron microscopy shows that amorphous layers, which can result from high-dose implantation, recrystallize between 800 and 1100 °C to very defective polycrystalline material. Lower-dose implants (down to 5 × 1013 cm – 2), which are not amorphous but defective after implantation, also anneal poorly up to 1100 °C, leaving a coarse network of extended defects. Despite such disorder, a high fraction of Te is found to be substitutional in GaN both following implantation and after annealing. Furthermore, although elevated-temperature implants result in less disorder after implantation, this damage is also impossible to anneal out completely by 1100 °C. The implications of this study are that considerably higher annealing temperatures will be needed to remove damage for optimum electrical properties. ©1998 American Institute of Physics.

Retinoic acid disrupts anterior ectodermal and endodermal development in ascidian larvae and postlarvae

In vertebrates, excess all-trans retinoic acid (RA) applied during axis formation leads to the apparent truncation of anterior structures. In this study we sought to determine the type of defects caused by ectopic RA on the development of the ascidian Herdmania curvata. We demonstrate that H. curvata embryos cultured in the presence of RA develop into larvae whose trunks are shortened and superficially resemble those of early metamorphosing postlarvae. Despite RA-treated larvae lacking papillar structures they respond normally to natural cues that induce metamorphosis, indicating that chemosensory functionality previously mapped to the most anterior region of normal larvae is unaffected by RA. Excess RA applied during postlarval development leads to a graded loss of the juvenile pharynx, apparently by respecifying anterior endoderm to a more posterior fate. This structure is considered homologous to the gill slits of amphioxus. which are also lost upon RA treatment. This suggests that RA may have had a role in the development of the pharynx of the ancestral chordate and that this function has been maintained in ascidians and cephalochordates and lost in vertebrates.

Computation of bifurcation boundaries for power systems: A new Delta-plane method

This paper is devoted to the problems of finding the load flow feasibility, saddle node, and Hopf bifurcation boundaries in the space of power system parameters. The first part contains a review of the existing relevant approaches including not-so-well-known contributions from Russia. The second part presents a new robust method for finding the power system load flow feasibility boundary on the plane defined by any three vectors of dependent variables (nodal voltages), called the Delta plane. The method exploits some quadratic and linear properties of the load now equations and state matrices written in rectangular coordinates. An advantage of the method is that it does not require an iterative solution of nonlinear equations (except the eigenvalue problem). In addition to benefits for visualization, the method is a useful tool for topological studies of power system multiple solution structures and stability domains. Although the power system application is developed, the method can be equally efficient for any quadratic algebraic problem.

The serotonin transporter gene and Parkinson's disease

Dysfunction in the serotonin (5-hydroxytryptamine) system and reduced serotonin concentrations have been reported in patients with Parkinson's disease (PD). Serotonin concentrations in neural tissue are controlled by a presynaptic serotonin transporter protein that is encoded by a single gene. Therefore, we investigated whether a polymorphic region in the serotonin transporter gene is associated with PD. Three variable-number tandem repeat (VNTR) elements of the serotonin transporter gene were detected by polymerase chain reaction, those with 9, 10, 11 and 12 copies of the repeat element. The 10-copy VNTR element was significantly less common in patients with PD than controls in the univariate analysis (p < 0.05). Logistic regression analysis revealed no significant differences between patients (n = 198) and controls (n = 200) in the distribution frequencies of 9-and 12-copy alleles and combined genotypes (odds ratio = 1.20; p = 1.71). A positive family history of PD was a strong predictor of disease risk (odds ratio = 2.98; 95% confidence interval 1.51-5.87; p = 0.001). Although slight differences were observed between patient and control groups, these data suggest that defects in serotonin concentrations in patients with PD are unlikely to be due to polymorphisms in the serotonin transporter gene in this large Australian cohort; however, the inverse association observed with the 10-copy allele warrants further investigation. Copyright (C) 2000 S. Karger AG, Basel.

Motor imagery in Parkinson's disease: A PET study

We used positron emission tomography (PET) with O-15-labelled water to record patterns of cerebral activation in six patients with Parkinson's disease (PD), studied when clinically off and after turning on as a result of dopaminergic stimulation. They were asked to imagine a Finger opposition movement performed with their right hand. externally paced at a rate of 1 Hz. Trials alternating between motor imagery and rest were measured. A pilot study of three age-matched controls was also performed. We chose the task as a robust method of activating the supplementary motor area (SMA), defects of which have been reported in PD. The PD patients showed normal de-rees of activation of the SMA (proper) when both off and on. Significant activation with imagining movement also occurred in the ipsilateral inferior parietal cortex (both off and when on) and ipsilateral premotor cortex (when off only). The patients showed significantly greater activation of the rostral anterior cingulate and significantly less activation of the left lingual gyrus and precuneus when performing the task on compared with their performance when off. PD patients when imagining movement and off showed less activation of several sites including the right dorsolateral prefrontal cortex (DLPFC) when compared to the controls performing the same task. No significant differences from controls were present when the patients imagined when on. Our results are consistent with other studies showing deficits of pre-SMA function in PD with preserved function of the SMA proper. In addition to the areas of reduced activation (anterior cingulate, DLPFC), there were also sites of activation (ipsilateral premotor and inferior parietal cortex) previously reported as locations of compensatory overactivity for PD patients performing similar tasks. Both failure of activation and compensatory changes a-re likely to contribute to the motor deficit in PD. (C) 2001 Movement Disorder Society.

Clinical and molecular genetics of myoclonic-astatic epilepsy and severe myoclonic epilepsy in infancy (Dravet syndrome)

The majority of severe epileptic encephalopathies of early childhood are symptomatic where a clear etiology is apparent. There is a small subgroup, however, where no etiology is found on imaging and metabolic studies, and genetic factors are important. Myoclonic-astatic epilepsy (MAE) and severe myoclonic epilepsy in infancy (SMEI), also known as Dravet syndrome, are epileptic encephalopathies where multiple seizure types begin in the first few years of life associated with developmental slowing. Clinical and molecular genetic studies of the families of probands with MAE and SMEI suggest a genetic basis. MAE was originally identified as part of the genetic epilepsy syndrome generalized epilepsy with febrile seizures plus (GEFS(+)). Recent clinical genetic studies suggest that SMEI forms the most severe end of the spectrum of the GEFS(+). GEF(+) has now been associated with molecular defects in three sodium channel subunit genes and a GABA subunit gene. Molecular defects of these genes have been identified in patients with MAE and SMEI. Interestingly, the molecular defects in MAE have been found in the setting of large GEFS(+) pedigrees, whereas, more severe truncation mutations arising de novo have been identified in patients with SMEI. It is likely that future molecular studies will shed light on the interaction of a number of genes, possibly related to the same or different ion channels, which result in a severe phenotype such as MAE and SMEI. (C) 2001 Elsevier Science B.V. All rights reserved.

Semisolid casting of AlSi7Mg0.35 alloy produced by low-temperature pouring

AlSi7Mg0.35 alloy was cast into permanent moulds using different pouring temperatures (725 to 625degreesC). As the pouring temperature decreased, the as-cast microstructure changed from a coarse dendritic structure, through fine equiaxed grains to fine rosette-like grains. The as-cast materials were then partially remelted and isothermally held at 580degreesC prior to semisolid casting into a stepped die. The feedstock material cast from a high temperature filled only half the die, with severe segregation and other defects. The low-temperature-poured material completely filled the die with negligible porosity. The quality of semisolid castings is significantly affected by the microstructure of the semisolid feedstock material that arises from a combination of as-cast and subsequent thermal treatment conditions. The paper describes (a) the influence of pouring temperature on the microstructure of feedstock; (b) microstructure evolution through remelting and (c) the quality of semisolid castings produced with this material. For A17Si0.35Mg alloy, low temperature pouring in the range of 625-650degreesC followed by suitable isothermal holding treatment can result in good quality semisolid casting.

Cytokines in the oral mucosa of mice infected with Candida albicans

Oropharyngeal candidiasis is associated with defects in cell-mediated immunity, and is commonly seen in immunocompromised patients. We have previously shown that T-cell-deficient BALB/c nude (nu/nu) mice are extremely susceptible to oropharyngeal candidiasis, and that recovery from a chronic infection is dependent on CD4 T lymphocytes. In this study we describe the local tissue cytokine profile in lymphocyte-reconstituted immunodeficient mice and their euthymic counterparts. Mice were infected orally with 10(8) cells of the yeast Candida albicans , and oral tissues sampled on days 0, 4, 8, and 14. Nude mice were reconstituted with 3 x 10(7) naive lymphocytes following oral inoculation. Interleukin (IL)-6, interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha were identified in the oral tissues of infected euthymic mice recovering from oral infection, as well as naive controls. TNF-alpha was identified in nude oral tissue on days 4 and 8, but only after lymphocyte reconstitution. No IL-2, IL-4 or IL-10 was detected in either euthymic or athymic mice at any time-point throughout the experiment. This study confirms the functional activity of T lymphocytes in reconstituted nude mice, and suggests that TNF-alpha may be an important mediator in the recovery from oropharyngeal candidiasis.