Split-gate quantum point contacts with tunable channel length

We report on developing split-gate quantum point contacts (QPCs) that have a tunable length for the transport channel. The QPCs were realized in a GaAs/AlGaAs heterostructure with a two- dimensional electron gas (2DEG) below its surface. The conventional design uses 2 gate fingers on the wafer surface which deplete the 2DEG underneath when a negative gate voltage is applied, and this allows for tuning the width of the QPC channel. Our design has 6 gate fingers and this provides additional control over the form of the electrostatic potential that defines the channel. Our study is based on electrostatic simulations and experiments and the results show that we developed QPCs where the effective channel length can be tuned from about 200 nm to 600 nm. Length-tunable QPCs are important for studies of electron many-body effects because these phenomena show a nanoscale dependence on the dimensions of the QPC channel

Big Cities, Big Problems? Reason for the Elderly to Move?

In many European countries, data on geographical patterns of internal elderly migration show that the elderly (55+) are more likely to leave than to move to the big cities. Besides emphasising the attractive features of the destination areas (pull factors), it is often assumed that this negative balance of migration of elderly people is caused by problems which mainly the big cities have to contend with and which would have a negative effect on living conditions, especially of the elderly (push factors). Although it is well-known that big cities in Europe are faced with several specific housing and neighbourhood problems, no detailed research has been carried out so far into whether these problems are indeed seen by the elderly themselves as very negative and, if so, whether these perceived problems result in an intention to move as a result of housing and neighbourhood dissatisfaction. The aim of this article is to shed empirical light on this matter for a case study in the Netherlands

Therapists' characteristics associated with the (non-)use of exposure in the treatment of anxiety disorders in youth:A survey among Dutch-speaking mental health practitioners

INTRODUCTION: Although there is consensus that exposure is the key ingredient in treating childhood anxiety disorders, several studies in the USA suggest exposure to be underused in clinical practice. Previous research pointed to therapists' beliefs about exposure, their age, experience, caseload, training and theoretical orientation, as well as the level of the therapists' own anxiety as important factors in the underusage of exposure in the treatment of adult anxiety disorders. This study examined what therapist characteristics may be involved in the (non-)use of exposure in treating childhood anxiety disorders. METHODS: An internet-based survey among 207 youth mental health care professionals in the Netherlands and Belgium was conducted to assess therapists' beliefs about exposure, their age, experience, caseload, training and theoretical orientation, as well as the level of the therapists' own anxiety, depression and stress. RESULTS: The current survey showed that therapists used exposure in about half of their cases of childhood anxiety and that the non-use was independently associated with the relatively strong negative beliefs about exposure, therapists' age, and non-CBT orientation. DISCUSSION: Findings point to the importance of addressing negative beliefs about exposure in therapists' training and supervision to resolve therapy drift away from exposure, and consequently improve utilization and delivery of exposure-based therapy for childhood anxiety disorders

Intelligent multimedia indexing and retrieval through multi-source information extraction and merging

This paper reports work on automated meta-data\ud creation for multimedia content. The approach results\ud in the generation of a conceptual index of\ud the content which may then be searched via semantic\ud categories instead of keywords. The novelty\ud of the work is to exploit multiple sources of\ud information relating to video content (in this case\ud the rich range of sources covering important sports\ud events). News, commentaries and web reports covering\ud international football games in multiple languages\ud and multiple modalities is analysed and the\ud resultant data merged. This merging process leads\ud to increased accuracy relative to individual sources

Evolution in the Dust Lane Fraction of Edge-on L* Spiral Galaxies since z=0.8

The presence of a well-defined and narrow dust lane in an edge-on spiral galaxy is the observational signature of a thin and dense molecular disk, in which gravitational collapse has overcome turbulence. Using a sample of galaxies out to z~1 extracted from the COSMOS survey, we identify the fraction of massive disks that display a dust lane. Our goal is to explore the evolution in the stability of the molecular ISM disks in spiral galaxies over a cosmic timescale. We check the reliability of our morphological classifications against changes in restframe wavelength, resolution, and cosmic dimming with (artificially redshifted) images of local galaxies from SDSS. We find that the fraction of L* disks with dust lanes in COSMOS is consistent with the local fraction (~80%) out to z~0.7. At z=0.8, the dust lane fraction is only slightly lower. A somewhat lower dust lane fraction in starbursting galaxies tentatively supports the notion that a high specific star formation rate can efficiently destroy or inhibit a dense molecular disk. A small subsample of higher redshift COSMOS galaxies display low internal reddening (E[B-V]), as well as a low incidence of dust lanes. These may be disks in which the growth of the dusty ISM disk lags behind that of the stellar disk. We note that at z=0.8, the most massive galaxies display a lower dust lane fraction than lower mass galaxies. A small contribution of recent mergers or starbursts to this most massive population may be responsible. The fact that the fraction of galaxies with dust lanes in COSMOS is consistent with little or no evolution implies that models to explain the Spectral Energy Distribution or the host galaxy dust extinction of supernovae based on local galaxies are still applicable to higher redshift spirals. It also suggests that dust lanes are long lived phenomena or can be reformed over very short time-scales.Comment: 14 pages, 9 figures, 2 tables, accepted for publication by Ap

Destruction of Molecular Hydrogen During Cosmological Reionization

We investigate the ability of primordial gas clouds to retain molecular hydrogen (H_2) during the initial phase of the reionization epoch. We find that before the Stromgren spheres of the individual ionizing sources overlap, the UV background below the ionization threshold is able to penetrate large clouds and suppress their H_2 abundance. The consequent lack of H_2 cooling could prevent the collapse and fragmentation of clouds with virial temperatures T_vir < 10^4 K (or masses 10^8 Msun [(1+z_vir)/10]^{-3/2}). This negative feedback on structure-formation arises from the very first ionizing sources, and precedes the feedback due to the photoionization heating.Comment: 14 pages, uuencoded compressed Postscript, 4 figures included. To appear in Ap

XTE J1550-564: INTEGRAL Observations of a Failed Outburst

The well known black-hole X-ray binary transient XTE J1550-564 underwent an outburst during the spring of 2003 which was substantially underluminous in comparison to previous periods of peak activity in that source. In addition, our analysis shows that it apparently remained in the hard spectral state over the duration of that outburst. This is again in sharp contrast to major outbursts of that source in 1998/1999 during which it exhibited an irregular light curve, multiple state changes and collimated outflows. This leads us to classify it as a "failed outburst." We present the results of our study of the spring 2003 event including light curves based on observations from both INTEGRAL and RXTE. In addition, we studied the evolution of the high-energy 3-300 keV continuum spectrum using data obtained with three main instruments on INTEGRAL. These spectra are consistent with typical low-hard-state thermal Comptonization emission. We also consider the 2003 event in the context of a multi-source, multi-event period-peak luminosity diagram in which it is a clear outlyer. We then consider the possibility that the 2003 event was due to a discrete accretion event rather than a limit-cycle instablility. In that context, we apply model fitting to derive the timescale for viscous propagation in the disk, and infer some physical characteristics.Comment: 22 pages, 8 figures, to be published in The Astrophysical Journa