Undoped gallium antimonide studied by positron annihilation spectroscopy

Positron lifetime spectroscopy has been used to study the vacancy type defects in undoped gallium antimonide. Temperature dependent positron trapping into the VGarelated defect having a characteristic lifetime of 310ps was observed in the as-grown sample. The lifetime data were well described by a model involving the thermal ionization (0/-) of the VGa-related defect and its ionization energy was found to be E(0/)=83meV. For the electron irradiated sample, the VGa-related defect with lifetime of 310ps that was found in the non-irradiated samples was also identified. Moreover, another lifetime component (280ps) was only observed in the electron irradiated sample but not in the non-irradiated sample. It was also attributed to the V Ga-related defect. The two identified VGa-related defects should have different microstructures because of their difference in characteristic lifetimes. The 280ps component remains thermally stable after the 500°C annealing while the 310ps component anneals at 300°C.published_or_final_versio

Microflow of fluorescently labelled red blood cells in tumours expressing single isoforms of VEGF and their response to VEGF-R tyrosine kinase inhibition

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.In this work we studied the functional differences between the microcirculation of murine tumours that only express single isoforms of vascular endothelial growth factor-A (VEGF), VEGF120 and VEGF188, and the effect of VEGF receptor tyrosine kinase (VEGF-R TK) inhibition on their functional response to the vascular disrupting agent, combretastatin A-4 phosphate (CA-4-P). We used measurement of fluorescentlylabelled red blood cell (RBC) velocities in tumour microvessels to study this functional response. RBC velocity for control VEGF120-expressing tumours was over 50% slower than for control VEGF188-expressing tumours, which may be due to the immature and haemorrhagic vasculature of the VEGF120 tumour. After chronic treatment with a VEGF-R tyrosine kinase inhibitor, SU5416, RBC velocities in VEGF120 tumours were significantly increased compared to control VEGF120 tumours, and similar to velocities in both VEGF188 treatment groups. Control and SU5416 treated VEGF188 tumours were not different from each other. Treatment of VEGF120 tumours with SU5416 reduced their vascular response to CA-4-P to a similar level to the VEGF188 tumours. Differential expression of VEGF isoforms not only affected vascular function in untreated tumours but also impacted on response to a vascular disrupting drug, CA-4-P, alone and in combination with an anti-angiogenic approach involving VEGF-R TK inhibition. Analysis of RBC velocities is a useful tool in measuring functional responses to vascular targeted treatments.This study is funded by the Cancer Research UK

FXN promoter silencing in the humanized mouse model of Friedreich Ataxia

Background - Friedreich ataxia is caused by an expanded GAA triplet-repeat sequence in intron 1 of the FXN gene that results in epigenetic silencing of the FXN promoter. This silencing mechanism is seen in patient-derived lymphoblastoid cells but it remains unknown if it is a widespread phenomenon affecting multiple cell types and tissues. Methodology / Principal Findings - The humanized mouse model of Friedreich ataxia (YG8sR), which carries a single transgenic insert of the human FXN gene with an expanded GAA triplet-repeat in intron 1, is deficient for FXN transcript when compared to an isogenic transgenic mouse lacking the expanded repeat (Y47R). We found that in YG8sR the deficiency of FXN transcript extended both upstream and downstream of the expanded GAA triplet-repeat, suggestive of deficient transcriptional initiation. This pattern of deficiency was seen in all tissues tested, irrespective of whether they are known to be affected or spared in disease pathogenesis, in both neuronal and non-neuronal tissues, and in cultured primary fibroblasts. FXN promoter function was directly measured via metabolic labeling of newly synthesized transcripts in fibroblasts, which revealed that the YG8sR mouse was significantly deficient in transcriptional initiation compared to the Y47R mouse. Conclusions / Significance- Deficient transcriptional initiation accounts for FXN transcriptional deficiency in the humanized mouse model of Friedreich ataxia, similar to patient-derived cells, and the mechanism underlying promoter silencing in Friedreich ataxia is widespread across multiple cell types and tissues.This research was supported by grants from the National Institutes of Health (R01 NS072418), and the Muscular Dystrophy Association to S.I.B. Y.K.C. is supported by a postdoctoral research fellowship from the Million Dollar Bike Ride Grant Program of the Orphan Disease Center at University of Pennsylvania. T.T.H. was supported by the American College of Medical Genetics Foundation. A.C.P. and M.G.M. were supported by the SURE and OSCTR programs at OUHSC, respectively

Intelligent spider for Internet searching

As World Wide Web (WWW) based Internet services become more popular, information overload also becomes a pressing research problem. Difficulties with searching on the Internet get worse as the amount of information that is available increases. A scalable approach to support Internet search is critical to the success of Internet services and other current or future national information infrastructure (NII) applications. A new approach to build an intelligent personal spider (agent), which is based on automatic textual analysis of Internet documents, is proposed. Best first search and genetic algorithm have been tested to develop the intelligent spider. These personal spiders are able to dynamically and intelligently analyze the contents of the users' selected homepages as the starting point to search for the most relevant homepages based on the links and indexing. An intelligent spider must have the capability to make adjustments according to progress of searching in order to be an intelligent agent. However, the current searching engines do not have communication between the users and the robots. The spider presented in the paper uses Java to develop the user interface such that the users can adjust the control parameters according to the progress and observe the intermediate results. The performances of the genetic algorithm based and best first search based spiders are also reported.published_or_final_versio

Nature of the acceptor responsible for p-type conduction in liquid encapsulated Czochralski-grown undoped gallium antimonide

The acceptors in undoped liquid encapsulated Czochralski (LEC)-grown GaSb were investigated using temperature dependent Hall (TDH) and positron lifetime spectroscopy measurements. TDH measurements were performed on nonirradiated and electron irradiated undoped samples. The 34 meV acceptor was found to be the important one responsible for the p-type conduction in nonirradiated and the e--irradiated undoped materials annealed at temperatures up to 500°C. This acceptor was not related to any VGa-related defect detected and was most likely the GaSb antisite.published_or_final_versio

Scheme for generating entangled states of two field modes in a cavity

This paper considers a two-level atom interacting with two cavity modes with equal frequencies. Applying a unitary transformation, the system reduces to the analytically solvable Jaynes-Cummings model. For some particular field states, coherent and squeezed states, the transformation between the two bare basis's, related by the unitary transformation, becomes particularly simple. It is shown how to generate, the highly non-classical, entangled coherent states of the two modes, both in the zero and large detuning cases. An advantage with the zero detuning case is that the preparation is deterministic and no atomic measurement is needed. For the large detuning situation a measurement is required, leaving the field in either of two orthogonal entangled coherent states.Comment: Accepted in J. Mod. Opt.; 12 pages; Replaced with revised version. Extended discussion of experimental realizations, earlier studies in the field and on the frequency dependence in the adiabatic eliminatio

Ion Larmor radius effects near a reconnection X line at the magnetopause: THEMIS observations and simulation comparison

We report a Time History of Events and Macroscale Interactions during Substorms (THEMIS-D) spacecraft crossing of a magnetopause reconnection exhaust ~9 ion skin depths (di) downstream of an X line. The crossing was characterized by ion jetting at speeds substantially below the predicted reconnection outflow speed. In the magnetospheric inflow region THEMIS detected (a) penetration of magnetosheath ions and the resulting flows perpendicular to the reconnection plane, (b) ion outflow extending into the magnetosphere, and (c) enhanced electron parallel temperature. Comparison with a simulation suggests that these signatures are associated with the gyration of magnetosheath ions onto magnetospheric field lines due to the shift of the flow stagnation point toward the low-density magnetosphere. Our observations indicate that these effects, ~2–3 di in width, extend at least 9 di downstream of the X line. The detection of these signatures could indicate large-scale proximity of the X line but do not imply that the spacecraft was upstream of the electron diffusion region

Detection and characterisation of β-globin gene cluster deletions in Chinese using multiplex ligationdependent probe amplification

Background: Deletions in the β-globin cluster causing thalassaemia and hereditary persistence of fetal haemoglobin (HPFH) are uncommon and difficult to detect. Data in Chinese are very scarce. Aims: To use a recently available technique to investigate the frequencies and nature of β-globin cluster deletions in Chinese. Methods: 106 subjects with phenotypes of thalassaemia or HPFH and suspected to have deletions in the β-globin cluster were studied. A commercially available kit employing multiplex ligation-dependent probe amplification (MLPA) was used to screen for deletions. Gap PCR and direct nucleotide sequencing were used to characterise deletions detected. Results: 17 deletions in the β-globin cluster were found in 17 patients: 8 of Chinese (Aγδβ)0 thalassaemia, 7 of Southeast Asian (Vietnamese) deletion and 2 of Thai (Aγδβ) 0 thalassaemia. The only type of deletion detected in δβ-thalassaemia was Chinese (Aγδβ) 0 thalassaemia. The deletional form of HPFH was rarely seen in only 1 case of Thai (Aγδβ)0 thalassaemia. Deletions presenting as β-thalassaemia trait and raised HbF were all of the Southeast Asian (Vietnamese) deletion type. When these deletions were co-inherited with classical β-thalassaemia mutations in compound heterozygous states, the phenotypes could be very variable. Conclusions: In the Chinese population, there are only relatively few types of deletions seen in the β-globin cluster. MLPA is a fast and effective way of screening for these deletions. Characterisation of these deletions allows the development of simpler and more specific PCR-based tests for routine diagnostic use. Accurate prediction of phenotype is not always feasible. The molecular defects in many cases of HPFH still await discovery.published_or_final_versio