Effect of a thin AlO_x layer on transition-edge sensor properties

We have studied the physics of transition-edge sensor (TES) devices with an insulating AlOx layer on top of the device to allow implementation of more complex detector geometries. By comparing devices with and without the insulating film, we have observed significant additional noise apparently caused by the insulator layer. In addition, AlOx was found to be a relatively good thermal conductor. This adds an unforeseen internal thermal feature to the system.Comment: 6 pages, 5 figures, Low Temperature Detectors 14 conferenc

Fluctuation superconductivity limited noise in a transition-edge sensor

In order to investigate the origin of the until now unaccounted excess noise and to minimize the uncontrollable phenomena at the transition in X-ray microcalorimeters we have developed superconducting transition-edge sensors into an edgeless geometry, the so-called Corbino disk (CorTES), with superconducting contacts in the centre and at the outer perimeter. The measured rms current noise and its spectral density can be modeled as resistance noise resulting from fluctuations near the equilibrium superconductor-normal metal boundaryComment: 9 pages, 4 figures.; Corrections to text and equations; replaced the affected figures. Added reference [12

Traumatic brain injury : relationships between brain structural abnormalities and cognitive function

Traumatic brain injury (TBI) is the leading cause of disability in young adults and a major public health problem. Persistent cognitive impairments are common, and constitute a significant source of long-term disability. The specific pathophysiological mechanisms underlying these impairments remain poorly understood. As it disconnects brain networks, white matter damage can be a key determinant of cognitive impairment after TBI. Neuroimaging and neuropsychological methods were employed to explore the relationships between indices of brain structure and cognitive function. The participants were 40 TBI patients and 40 healthy controls. First, relationships between focal lesions and cognitive performance were investigated using structural magnetic resonance imaging (MRI) and a battery of neuropsychological tests. The results demonstrated that lesion location and load are not good indices of the cognitive deficits - probably because diffuse axonal injury is poorly assessed by standard MRI. By contrast, diffusion tensor imaging (DTI) can be used to quantify the microstructure of white matter. A ‘whole-brain’ technique, tract-based spatial statistics (TBSS), was used to flexibly analyse the structure of white matter tracts. Despite only small amounts of focal damage observed using standard MRI, TBSS revealed widespread white matter abnormalities after TBI. White matter damage was found in patients with no evidence of focal damage, and in patients classified as ‘mild’ clinically. Relationships between white matter tract structure and specific cognitive functions were then explored. The structure of the fornix, an important white matter pathway of the hippocampus, correlated with verbal associative memory across the patient and control groups. By contrast, structure of frontal lobe connections showed distinct relationships with executive function in these two groups. The results emphasise the importance of white matter pathology after TBI and suggest that disruption to specific white matter tracts is associated with particular patterns of cognitive impairment, but also highlight the complexity of these relationships.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Readout of solid-state charge qubits using a single-electron pump

A major difficulty in realizing a solid-state quantum computer is the reliable measurement of the states of the quantum registers. In this paper, we propose an efficient readout scheme making use of the resonant tunneling of a ballistic electron produced by a single electron pump. We treat the measurement interaction in detail by modeling the full spatial configuration, and show that for pumped electrons with suitably chosen energy the transmission coefficient is very sensitive to the qubit state. We further show that by using a short sequence of pumping events, coupled with a simple feedback control procedure, the qubit can be measured with high accuracy.Comment: 5 pages, revtex4, 4 eps figures. v2: published versio

Traumatic brain injury: relationships between brain structural abnormalities and cognitive function

Traumatic brain injury (TBI) is the leading cause of disability in young adults and a major public health problem. Persistent cognitive impairments are common, and constitute a significant source of long-term disability. The specific pathophysiological mechanisms underlying these impairments remain poorly understood. As it disconnects brain networks, white matter damage can be a key determinant of cognitive impairment after TBI. Neuroimaging and neuropsychological methods were employed to explore the relationships between indices of brain structure and cognitive function. The participants were 40 TBI patients and 40 healthy controls. First, relationships between focal lesions and cognitive performance were investigated using structural magnetic resonance imaging (MRI) and a battery of neuropsychological tests. The results demonstrated that lesion location and load are not good indices of the cognitive deficits - probably because diffuse axonal injury is poorly assessed by standard MRI. By contrast, diffusion tensor imaging (DTI) can be used to quantify the microstructure of white matter. A ‘whole-brain’ technique, tract-based spatial statistics (TBSS), was used to flexibly analyse the structure of white matter tracts. Despite only small amounts of focal damage observed using standard MRI, TBSS revealed widespread white matter abnormalities after TBI. White matter damage was found in patients with no evidence of focal damage, and in patients classified as ‘mild’ clinically. Relationships between white matter tract structure and specific cognitive functions were then explored. The structure of the fornix, an important white matter pathway of the hippocampus, correlated with verbal associative memory across the patient and control groups. By contrast, structure of frontal lobe connections showed distinct relationships with executive function in these two groups. The results emphasise the importance of white matter pathology after TBI and suggest that disruption to specific white matter tracts is associated with particular patterns of cognitive impairment, but also highlight the complexity of these relationships

Normal metal - superconductor decoupling as a source of thermal fluctuation noise in transition-edge sensors

We have studied the origin of excess noise in superconducting transition-edge sensors (TES) with several different detector designs. We show that most of the observed noise and complex impedance features can be explained by a thermal model consisting of three bodies. We suggest that one of the thermal blocks and the corresponding thermal fluctuation noise arises due to the high-frequency thermal decoupling of the normal and superconducting phase regions inside the TES film. Our results are also consistent with the prediction that in thin bilayer proximitized superconductors, the jump in heat capacity at the critical temperature is smaller than the universal BCS theory result.Comment: 11 pages 14 figure

Discovery of a New Deeply Eclipsing SU UMa-Type Dwarf Nova, IY UMa (= TmzV85)

We discovered a new deeply eclipsing SU UMa-type dwarf nova, IY UMa, which experienced a superoutburst in 2000 January. Our monitoring revealed two distinct outbursts, which suggest a superoutburst interval of ~800 d, or its half, and an outburst amplitude of 5.4 mag. From time-series photometry during the superoutburst, we determined a superhump and orbital period of 0.07588 d and 0.0739132 d, respectively.Comment: 5 pages, 3 figures, accepted by PASJ lette

Heavy MSSM Higgs Bosons at CMS: "LHC wedge" and Higgs-Mass Precision

The search for MSSM Higgs bosons will be an important goal at the LHC. In order to analyze the search reach of the CMS experiment for the heavy neutral MSSM Higgs bosons, we combine the latest results for the CMS experimental sensitivities based on full simulation studies with state-of-the-art theoretical predictions of MSSM Higgs-boson properties. The experimental analyses are done assuming an integrated luminosity of 30 or 60 fb^-1. The results are interpreted as 5 \si discovery contours in MSSM M_A-tan_beta benchmark scenarios. Special emphasis is put on the variation of the Higgs mixing parameter mu. While the variation of mu can shift the prospective discovery reach (and correspondingly the ``LHC wedge'' region) by about Delta tan_beta= 10, the discovery reach is rather stable with respect to the impact of other supersymmetric parameters. Within the discovery region we analyze the accuracy with which the masses of the heavy neutral Higgs bosons can be determined. An accuracy of 1-4% should be achievable, depending on M_A and tan_beta.Comment: Talk given by G.W. at EPS07 (Manchester, July 2007) and talk given by S.H. at SUSY07 (Karlsruhe, July 2007). 4 pages, 2 figure

WZ Sge-Type Star V592 Herculis

We observed the entire course of the 1998 outburst of V592 Her, which was originally reported as a nova in 1968. We have been able to construct a full light curve of the outburst, which is characterized by a rapid initial decline (0.98 mag/d), which smoothly developed into a plateau phase with a slower linear decline. We detected superhumps characteristic to SU UMa-type dwarf novae ~7 d after the optical maximum. The overall behavior of the light curve and the development of superhumps were characteristic to a WZ Sge-type dwarf nova. Combined with the past literature, we have been able to uniquely determine the superhump period to be 0.05648(2) d. From this period, together with a modern interpretation of the absolute magnitude of the outburst light curve, we conclude that the overall picture of V592 Her is not inconsistent with a lower main-sequence secondary star in contrast to a previous claim that V592 Her contains a brown dwarf.Comment: 10 pages, 7 figures, accepted for publication in Publ. Astron. Soc. Japa