Collective charge-density excitations of non-circular quantum dots in a magnetic field

Recent photoabsorption measurements have revealed a rich fine structure in the collective charge-density excitation spectrum of few-electron quantum dots in the presence of magnetic fields. We have performed systematic computational studies of the far-infrared density response of quantum dots, using time-dependent density-functional theory in the linear regime and treating the dots as two-dimensional disks. It turns out that the main characteristics observed in the experiment can be understood in terms of the electronic shell structure of the quantum dots. However, new features arise if a breaking of the circular symmetry of the dots is allowed, leading to an improved description of the experimental results.Comment: 18 pages, 5 figures, submitted to Phys. Rev.

Quantum Computation with Quantum Dots and Terahertz Cavity Quantum Electrodynamics

A quantum computer is proposed in which information is stored in the two lowest electronic states of doped quantum dots (QDs). Many QDs are located in a microcavity. A pair of gates controls the energy levels in each QD. A Controlled Not (CNOT) operation involving any pair of QDs can be effected by a sequence of gate-voltage pulses which tune the QD energy levels into resonance with frequencies of the cavity or a laser. The duration of a CNOT operation is estimated to be much shorter than the time for an electron to decohere by emitting an acoustic phonon.Comment: Revtex 6 pages, 3 postscript figures, minor typos correcte

Time course of cerebral oxygenation and cerebrovascular reactivity in Kyrgyz highlanders. A five-year prospective cohort study

Introduction: This prospective cohort study assessed the effects of chronic hypoxaemia due to high-altitude residency on the cerebral tissue oxygenation (CTO) and cerebrovascular reactivity.Methods: Highlanders, born, raised, and currently living above 2,500 m, without cardiopulmonary disease, participated in a prospective cohort study from 2012 until 2017. The measurements were performed at 3,250 m. After 20 min of rest in supine position while breathing ambient air (FiO$_{2}$ 0.21) or oxygen (FiO$_{2}$ 1.0) in random order, guided hyperventilation followed under the corresponding gas mixture. Finger pulse oximetry (SpO$_{2}$) and cerebral near-infrared spectroscopy assessing CTO and change in cerebral haemoglobin concentration (cHb), a surrogate of cerebral blood volume changes and cerebrovascular reactivity, were applied. Arterial blood gases were obtained during ambient air breathing.Results: Fifty three highlanders, aged 50 ± 2 years, participated in 2017 and 2012. While breathing air in 2017 vs. 2012, PaO$_{2}$ was reduced, mean ± SE, 7.40 ± 0.13 vs. 7.84 ± 0.13 kPa; heart rate was increased 77 ± 1 vs. 70 ± 1 bpm (p < 0.05) but CTO remained unchanged, 67.2% ± 0.7% vs. 67.4% ± 0.7%. With oxygen, SpO$_{2}$ and CTO increased similarly in 2017 and 2012, by a mean (95% CI) of 8.3% (7.5–9.1) vs. 8.5% (7.7–9.3) in SpO$_{2}$, and 5.5% (4.1–7.0) vs. 4.5% (3.0–6.0) in CTO, respectively. Hyperventilation resulted in less reduction of cHb in 2017 vs. 2012, mean difference (95% CI) in change with air 2.0 U/L (0.3–3.6); with oxygen, 2.1 U/L (0.5–3.7).Conclusion: Within 5 years, CTO in highlanders was preserved despite a decreased PaO$_{2}$. As this was associated with a reduced response of cerebral blood volume to hypocapnia, adaptation of cerebrovascular reactivity might have occurred

A Two-Dimensional Electron Gas as a Sensitive Detector for Time-Resolved Tunneling Measurements on Self-Assembled Quantum Dots

A two-dimensional electron gas (2DEG) situated nearby a single layer of self-assembled quantum dots (QDs) in an inverted high electron mobility transistor (HEMT) structure is used as a detector for time-resolved tunneling measurements. We demonstrate a strong influence of charged QDs on the conductance of the 2DEG which allows us to probe the tunneling dynamics between the 2DEG and the QDs time resolved. Measurements of hysteresis curves with different sweep times and real-time conductance measurements in combination with an boxcar-like evaluation method enables us to unambiguously identify the transients as tunneling events between the s- and p-electron QD states and the 2DEG and rule out defect-related transients

SNAI2/Slug promotes growth and invasion in human gliomas

<p>Abstract</p> <p>Background</p> <p>Numerous factors that contribute to malignant glioma invasion have been identified, but the upstream genes coordinating this process are poorly known.</p> <p>Methods</p> <p>To identify genes controlling glioma invasion, we used genome-wide mRNA expression profiles of primary human glioblastomas to develop an expression-based rank ordering of 30 transcription factors that have previously been implicated in the regulation of invasion and metastasis in cancer.</p> <p>Results</p> <p>Using this approach, we identified the oncogenic transcriptional repressor, <it>SNAI2</it>/Slug, among the upper tenth percentile of invasion-related transcription factors overexpressed in glioblastomas. <it>SNAI2 </it>mRNA expression correlated with histologic grade and invasive phenotype in primary human glioma specimens, and was induced by EGF receptor activation in human glioblastoma cells. Overexpression of <it>SNAI2/</it>Slug increased glioblastoma cell proliferation and invasion <it>in vitro </it>and promoted angiogenesis and glioblastoma growth <it>in vivo</it>. Importantly, knockdown of endogenous <it>SNAI2</it>/Slug in glioblastoma cells decreased invasion and increased survival in a mouse intracranial human glioblastoma transplantation model.</p> <p>Conclusion</p> <p>This genome-scale approach has thus identified <it>SNAI2</it>/Slug as a regulator of growth and invasion in human gliomas.</p

Transport spectroscopy of non-equilibrium many-particle spin states in self-assembled quantum dots

Self-assembled quantum dots (QDs) are prominent candidates for solid-state quantum information processing. For these systems, great progress has been made in addressing spin states by optical means. In this study, we introduce an all-electrical measurement technique to prepare and detect non-equilibrium many-particle spin states in an ensemble of self-assembled QDs at liquid helium temperature. The excitation spectra of the one- (QD hydrogen), two- (QD helium) and three- (QD lithium) electron configuration are shown and compared with calculations using the exact diagonalization method. An exchange splitting of 10 meV between the excited triplet and singlet spin states is observed in the QD helium spectrum. These experiments are a starting point for an all-electrical control of electron spin states in self-assembled QDs above liquid helium temperature

Loss of NOTCH2 Positively Predicts Survival in Subgroups of Human Glial Brain Tumors

The structural complexity of chromosome 1p centromeric region has been an obstacle for fine mapping of tumor suppressor genes in this area. Loss of heterozygosity (LOH) on chromosome 1p is associated with the longer survival of oligodendroglioma (OD) patients. To test the clinical relevance of 1p loss in glioblastomas (GBM) patients and identifiy the underlying tumor suppressor locus, we constructed a somatic deletion map on chromosome 1p in 26 OG and 118 GBM. Deletion hotspots at 4 microsatellite markers located at 1p36.3, 1p36.1, 1p22 and 1p11 defined 10 distinct haplotypes that were related to patient survival. We found that loss of 1p centromeric marker D1S2696 within NOTCH2 intron 12 was associated with favorable prognosis in OD (P = 0.0007) as well as in GBM (P = 0.0175), while 19q loss, concomitant with 1p LOH in OD, had no influence on GBM survival (P = 0.918). Assessment of the intra-chromosomal ratio between NOTCH2 and its 1q21 pericentric duplication N2N (N2/N2N-test) allowed delineation of a consistent centromeric breakpoint in OD that also contained a minimally lost area in GBM. OD and GBM showed distinct deletion patterns that converged to the NOTCH2 gene in both glioma subtypes. Moreover, the N2/N2N-test disclosed homozygous deletions of NOTCH2 in primary OD. The N2/N2N test distinguished OD from GBM with a specificity of 100% and a sensitivity of 97%. Combined assessment of NOTCH2 genetic markers D1S2696 and N2/N2N predicted 24-month survival with an accuracy (0.925) that is equivalent to histological classification combined with the D1S2696 status (0.954) and higher than current genetic evaluation by 1p/19q LOH (0.762). Our data propose NOTCH2 as a powerful new molecular test to detect prognostically favorable gliomas