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We present the synthesis of a novel binary metal oxide material: Ba

We present the synthesis of a novel binary metal oxide material: Ba7Mn4O15. The crystal structure has been investigated by high-resolution powder synchrotron X-ray diffraction in the temperature range of 100–300 K as well as by powder neutron diffraction at 10 and 80 K. This material represents an isostructural barium-substituted analogue of the layered material Sr7Mn4O15 that forms its own structural class. However, we find that Ba7Mn4O15 adopts a distinct magnetic ordering, resulting in a magnetoelectric ground state below 50 K. The likely magnetoelectric coupling mechanisms have been inferred from performing a careful symmetry-adapted refinement against the powder neutron diffraction experiments, as well as by making a comparison with the nonmagnetoelectric ground state of Sr7Mn4O15.

The orthorhombic mineral moolooite, CuC2O4. nH2O, described by Clarke and Williams (1986) using Debye-Scherrer photographic data, has a fully-disordered stacking fault (FDSF) structure. Related monoclinic models have been reported for various synthesised samples based on Schmittler (1968). In the present study, synchrotron radiation diffraction data for moolooite and synthesised specimens have been examined with particular reference to crystallographic disorder. The moolooite data correspond to space group Pnnm, with a = 5.3064(2), b = 5.6804(2), c = 2.5630(1) Å; Vc = 77.26(1) Å3; and Z = 1; and the FDSF structure along the b-direction has been confirmed. The synthetic specimen data from the study indicate partial ordering, with space group P21/n; and the cell parameters for one specimen being a = 5.957(7), b = 5.611(5), c = 5.133(7) Å; β = 115.16(2)°; Vc = 155.27 Å3 and Z = 2. The level of zeolitic water in the materials has been considered using the approach of Schmittler based on thermogravimetry and pycnometry. The new data for natural topotype material correspond to CuC2O4.1.0H2O. It is postulated that the level of water for natural and synthetic specimens may be attributed to the conditions under which the material forms.

The Cryogenic Dark Matter Search (CDMS) experiment employs ultra-cold solid-state detectors to search for rare events resulting from WIMP-nucleus scattering. An innovative detector packaging and readout system has been developed to meet the unusual combination of requirements for: low temperature, low radioactivity, low energy threshold, and large channel count. Features include use of materials with low radioactivity such as multi-layer KAPTON laminates for circuit boards; immunity to microphonic noise via a vacuum coaxial wiring design, manufacturability, and modularity. The detector readout design had to accommodate various electronic components which have to be operated in close proximity to the detector as well maintaining separate individual temperatures (ranging from 600 mK to 150 K) in order to achieve optimal noise performance. The paper will describe the general electrical, thermal, and mechanical designs of the CDMS readout system, as well as presenting the theoretical and measured performance of the detector readout channels.

CD8 + T-cell persistence can be seen in ganglia harboring latent herpes simplex virus (HSV) infection. While there is some evidence that these cells suppress virus reactivation, this view remains controversial. Given that maintenance of latency by CD8 + T cells would necessitate ongoing exposure to antigen within this site, we sought evidence for such chronic stimulation. Initial experiments showed infiltration by activated but not naïve CD8 + T cells into ganglia harboring latent HSV infection. While such infiltration was independent of T-cell specificity, once recruited, only virus-specific T cells expressed high levels of preformed granzyme B, a marker of ongoing activation. Moreover, bone marrow replacement chimeras showed that these elevated granzyme levels were totally dependent on presentation by parenchymal cells within the ganglia. Overall, this study argues that activated CD8 + T cells are nonspecifically recruited into latently infected ganglia, and in this site they are exposed to ongoing antigen stimulation, most likely by infected neuronal cells.

In the past year and a half, the Cryogenic Dark Matter Search (CDMS) collaboration has been active at the Soudan mine in installing a system for running ZIP detectors that will be used to search for dark matter in the form of Weakly Interacting Massive Particles. Presently, there is an operating cryogenic system, working electronics, a functional data acquisition and analysis system, passive shielding, an active muon veto, and 12 ZIP detectors. Six of the 12 ZIP detectors have been tested in situ and are fully operational with acceptable noise profiles. CDMS is in the process of commissioning the experiment and expects to be making a background measurement by the end of summer 2003.

The Cryogenic Dark Matter Search (CDMS) uses low-temperature Ge and Si detectors to search for Weakly Interacting Massive Particles (WIMPs) via their elastic-scattering interaction with atomic nuclei while discriminating against interactions of background particles. CDMS data from 1998 and 1999 with a relaxed fiducial-volume cut (resulting in 15.8 kg-days exposure on Ge) are consistent with an earlier analysis with a more restrictive fiducial-volume cut. Twenty-three WIMP candidate events are observed, but these events are consistent with a background from neutrons. Resulting limits on the spin-independent WIMP-nucleon elastic-scattering cross-section are lower than those of any other experiment for WIMPs with masses between 10–70 GeV c −2 . Under the assumptions of standard WIMP interactions and a standard halo, the results are incompatible with the annual-modulation signal of DAMA at 99.99% CL in the asymptotic limit.

We present the recent progress using transition-edge sensors (TES) for cryogenic particle detectors. First, by directly absorbing photons in tungsten TES devices, an instrument has been made which time stamps ( 0.1 μs ) and energy resolves (0.15 eV FWHM) each photon at rates up to 10 kHz. Observations of the Crab pulsar are the first broad spectrum infrared through full optical and time resolved on any astronomical object. Second, in the CDMS (cryogenic dark matter search) experiment looking for WIMPs, large crystals of silicon and germanium are instrumented with QET (quasiparticle-trap-assisted electrothermal-feedback transition-edge sensors) phonon sensors which provide the recoil energy and location in x,y and z for each event. Together with an ionization readout, these detectors provide powerful discrimination capabilities against known backgrounds and they are now probing new regions for WIMP dark matter.

The last year saw major progress in the development of the nuclear-recoil dark matter detector for the Cryogenic Dark Matter Search (CDMS II) experiment. The basic γ-ray background discrimination is based on ionization yield. However, as shown in separate experiments, surface events and especially electrons also results in low ionization yield due to incomplete charge collection. The two-fold strategy to reduce these unwanted backgrounds was to improve charge collection at the detector surface and to employ fast phonon sensors on Ge. A 250 g Ge detector with an Al Schottky contact on an amorphous Si blocking layer and a Quasiparticle-trap-assisted Electrothermal-feedback Transition-edge (QET) phonon sensor has been characterized. The phonon collection efficiency of the new detector is similar to that of the latest 100 g Si Fast Large Ionization and Phonon (FLIP) detector, which has the same phonon sensor design. The fall times of the phonon pulses are longer and consistent with simulations. The charge collection at the surface is high and very similar to that of smaller test devices and the last revision of Berkeley Large Ionization and Phonon (BLIP) detectors. The four fast non-thermal phonon sensors yield x, y position resolution similar to the Si FLIP detector. A rise time surface effect was demonstrated on both sides of the detector. The effect results in a much more effective rejection of surface events than the rejection based on charge yield alone and therefore improves the sensitivity for a dark matter search.

The Cryogenic Dark Matter Search (CDMS) ZIP detectors utilize quasiparticle trapping as the mechanism for coupling the energy of a particle interaction in the Ge (or Si) absorber into a tungsten (W) transition edge sensor (TES). Consequently, the dynamics of quasiparticle propagation and loss significantly impact the energy collection and resolution of the detector. This paper describes the considerations necessary in optimizing the detector surface geometry in order to have maximal quasiparticle collection.

The Cryogenic Dark Matter Search (CDMS) employs massive ionization- and phonon-mediated detectors to search for WIMPs via their elastic scattering interactions with nuclei while discriminating against interactions by other background particles. Limits on the WIMP-nucleon scattering cross-section, based on 3.1 kg d of exposure, exclude new parameter space in the 10–30 GeV WIMP mass region and also a portion of the region allowed by the DAMA annual modulation search (Bernabei, Phys. Lett. 450 (1999) 448).

Superconducting transition edge sensors (TESs) are showing promise for the wide-band spectroscopy of individual photons from the mid-infrared (IR), through the optical, and into the near ultraviolet (UV). Our TES sensors are ∼20 μm square, 40 nm thick tungsten (W) films with a transition temperature of about 80 mK. We typically attain an energy resolution of 0.15 eV FWHM over the optical range with relative timing resolution of 100 ns. Single photon events with sub-microsecond risetimes and few microsecond falltimes have been achieved allowing count rates in excess of 30 kHz per pixel. Additionally, tungsten is approximately 50% absorptive in the optical (dropping to 10% in the IR) giving these devices an intrinsically high quantum efficiency. These combined traits make our detectors attractive for fast spectrophotometers and photon-starved applications such as wide-band, time and energy resolved astronomical observations. We present recent results from our work toward the fabrication and testing of the first TES optical photon imaging arrays.

We have measured the effects of dilute magnetic-atom doping on the superconducting transition temperature of tungsten thin films. Our “Tc tuning” technique is accurate, precise, and simple. Experiments were performed using dc-magnetron-sputtered tungsten films with undoped values of Tc in the range of 70–150 mK. The magnetic-atom doping was achieved using ion implantation. Specific Tc suppressions of between 5% and 65% were targeted and observed in this study. The transition width of each undoped sample was ≈1 mK and the transition widths remained sharp after implantation with 56Fe+ ions. Our data are in good agreement with predictions of a linear dependence of Tc suppression with increasing magnetic-atom concentration, in the small concentration limit. At higher concentrations, antiferromagnetic coupling between the magnetic dopant atoms becomes important and the Tc-suppression effect is diminished. We use our Tc data to calculate the Abrikosov–Gor’kov (AG) and Ruderman–Kittel–Kasuya–Yosida (RKKY) spin–f...

We have recently demonstrated wideband detection of individual photons from the mid infrared (IR), through the optical, and into the near ultraviolet (UV). We use thin film tungsten transition edge sensors about 20 /spl mu/m on a side to detect single photon events above a noise threshold of 0.3 eV (4 /spl mu/m wavelength), with an energy resolution of 0.12 eV FWHM (full width at half maximum). The observed events have a risetime (falltime) of 0.5 /spl mu/s (30 /spl mu/s). In this paper we present a summary of recent calibration data and resolution measurements as well as two proof-of-principle experiments to show the ability of TES detectors to extract both time and energy information from photons arriving at the detector during astronomical observations.

We have developed a new operating mode for superconducting transition edge sensors (TES) used in cryogenic particle detection which use electrothermal feedback (ETF). By using the new technique with the optical photon detectors our group has developed, we have been able to reduce the decay time of the pulses from the detector by more than a factor of five. The technique involves reducing the voltage bias across the tungsten superconducting detector during a pulse. By reducing the voltage during a pulse, there is an additional reduction in joule heating which speeds up the recovery of the detector. In theory, the technique reduces the decay time of the pulses which allows for higher maximum count rates. In addition to a brief theoretical analysis of the benefits of the technique, we present experimental results and analysis demonstrating a pulse decay time reduction by a factor of five.

The Cryogenic Dark Matter Search experiment uses cooled germanium and silicon detectors for a direct search for weakly interacting massive particles in our Galaxy. The novel detectors allow a high degree of background rejection by discriminating between electron and nuclear recoils through the simultaneous measurement of the energy deposited in phonons and ionization. Exposures on the order of one kilogram-day from initial runs of our experiment yield (preliminary) upper limits on the WIMP-nucleon cross section that are comparable to much longer runs of other experiments. Current and future runs promise significant improvement, primarily due to improved detectors and reduced surface-electron backgrounds.

The binding of lithium and boron, at normal physiological levels, to plasma proteins has been investigated by the techniques of precipitation with ethyl alcohol and gel chromatography. Assays of lithium and boron were made by thermal neutron activation and mass spectrometric assay of 3He and 4He. Results of alcohol precipitation experiments for plasma from two apparently healthy donors showed that 13+/-4% and 16+/-3% of the lithium in plasma is protein bound, but essentially no boron is bound under the conditions used. We believe that because of denaturation of proteins which occurs during alcohol precipitation, these percentages represent lithium and boron tightly bound to protein molecules. The results of the gel-chromatography experiment, on the other hand, showed that lithium and boron are bound to a wide range of plasma proteins, from low (approximately 60,000 amu) to high (approximately 1,000,000 amu) molecular weights, and to very low- (approximately 6000 amu) molecular-weight ligands. Although a clear identification of the specific proteins which bind lithium and boron cannot be made at present, some possibilities can be suggested.

We have demonstrated a new type of phonon sensor for cryogenic particle detectors with high-bandwidth SQUID readout. Our Quasiparticle-trap assisted Electrothermal feedback Transition edge sensor (QET) utilizes aluminum quasiparticle traps attached to a tungsten superconducting transition edge sensor patterned on a silicon substrate. The tungsten lines are voltage biased and self-regulate in the transition region. Phonons from particle interactions in the silicon deposit energy into the creating quasiparticles. The quasiparticles are trapped into the tungsten and cause its electrical resistance to increase. The resulting decrease in current through the sensor is measured with a DC SQUID array. We have been able to demonstrate xy-position resolution of /spl sim/0.3 mm for 6 keV X-rays from an /sup 55/Fe source in a 2 cm/spl times/2 cm/spl times/4 mm (4 g) detector. We describe our optimizations of the sensor design for improved energy and position. By simultaneously measuring the ionization yield we have demonstrated discrimination between electron and nuclear recoil events in a 100 g Si detector for the CDMS (Cryogenic Dark Matter Search) experiment.

Until recently, our work on superconducting thin film phonon sensors for cryogenic detector applications was limited to silicon substrates only. We have now successfully extended low T/sub c/ (/spl les/100 mK) tungsten sensor technology and sensor fabrication capability to include high purity germanium substrates as well. Here, we describe a technique for fabricating low T/sub c/ superconducting tungsten films on germanium, and we present first results from cryogenic characterization experiments with these films. We also summarize our work on the development of a process to independently etch aluminum and tungsten films deposited on the same germanium substrate. The capability to selectively etch aluminum and tungsten films is critical for the fabrication of our silicon and soon also germanium detectors which utilize overlapping thin films of superconducting tungsten and aluminum for the phonon sensors. Due to the nature of their operation, we refer to these sensors as W/Al Quasiparticle trap assisted-Electrothermal feedback-Transition edge (QET) Sensors.

We investigated the low temperature transport properties of AlGaAs/GaAs quantum dot arrays. The coupling between dots and the electron density are controlled by a single gate covering the array. Below 1 K, the current - voltage (I - V) curves show multiple discontinuous jumps in the current, or `switching events', between different insulating and conducting states, which occur at gate-voltage and temperature dependent thresholds. Each single switching event is accompanied by hysteresis, and multiple switching events result in a hierarchy of hysteresis loops. A possible mechanism for this behavior, involving gate-to-dot tunneling, is discussed.

We present an overview of the low temperature detectors being developed for dark matter searches. The important background discrimination techniques are discussed. In addition, we describe recent advances in the athermal phonon detectors being developed by our group at Stanford.

We report on progress of the CDMS experiment, which seeks to detect WIMP dark matter through its interactions in a particle detector operated in a low radioactivity environment. We have developed novel cryogenic detectors which discriminate between nuclear recoils from WIMPs and electron recoils from background photons. We describe the experiment and discuss recent progress, including first operation of a cryogenic detector in the low radioactivity cryostat in June of 1996.

Charge collection efficiency measurements in silicon detectors at low temperature (T

We discuss the status of a cryogenic dark matter search beginning operation in the Stanford Underground Facility. The detectors will be cooled in a specially designed cryostat connected to a modified side access Oxford 400 dilution refrigerator. We discuss two detector designs and performance, the cryostat construction and operation, and the multi-level shield surrounding the cryostat. Finally, we will examine the limits which we will be able to set on WIMP dark matter with this experiment.

We have investigated the effect of thin SiO 2 sublayers on the transmission of phonons into titanium transition edge sensors (TESs) fabricated on high-resistivity (100) float zone (FZ) silicon substrates. The response of a TES on native oxide is compared to that of an adjacent TES on a thermally grown SiO 2 sublayer. Latching current measurements indicate that thermal phonons are not attenuated by the film. However, pulse data from X-ray scattering experiments suggest that high frequency phonons are preferentially scattered.

We investigate low temperature transport in $200\ifmmode\times\else\texttimes\fi{}200$ arrays of GaAs quantum dots in which coupling between dots and electron density is controlled by a single gate. Current-voltage curves obey a power law above a threshold voltage with exponent $\ensuremath{\sim}1.5$, and show discontinuous and hysteretic jumps in the current, or ``switching events.'' Multiple switching events result in a hierarchy of hysteresis loops. Switching and hysteresis decrease with increasing temperature and disappear above 1 K. A possible mechanism for the hysteresis involving gate-to-dot tunneling is discussed.

We report measurements of universal-like conductance fluctuations in a quasiballistic approximately 2 mu m2 GaAs/AlGaAs quantum dot with adjustable point contact leads. Measurements cover a range of conductance G from nearly isolated, (G) approximately 0.1e2/h, to several modes in each lead, (G) approximately 5e2/h. The characteristic magnetic field scale of the fluctuations is found to increase with increasing mean conductance through the dot, consistent with a semiclassical picture of escape through the leads, and provides a means of estimating the phase breaking time tau phi for electrons inside the dot. The fluctuation amplitude is found to increase with increasing dot conductance, then begins to saturate once a few conducting channels are open.

Data taken during the final shallow-site run of the first tower of the Cryogenic Dark Matter Search (CDMS II) detectors have been reanalyzed with improved sensitivity to small energy depositions. Four ~224 g germanium and two ~105 g silicon detectors were operated at the Stanford Underground Facility (SUF) between December 2001 and June 2002, yielding 118 live days of raw exposure. Three of the germanium and both silicon detectors were analyzed with a new low-threshold technique, making it possible to lower the germanium and silicon analysis thresholds down to the actual trigger thresholds of ~1 keV and ~2 keV, respectively. Limits on the spin-independent cross section for weakly interacting massive particles (WIMPs) to elastically scatter from nuclei based on these data exclude interesting parameter space for WIMPs with masses below 9 GeV/c^2. Under standard halo assumptions, these data partially exclude parameter space favored by interpretations of the DAMA/LIBRA and CoGeNT experiments' data as WIMP signals, and exclude new parameter space for WIMP masses between 3 GeV/c^2 and 4 GeV/c^2., 18 pages, 12 figures, 5 tables

We present evidence of an enhanced ballistic phonon component resulting from surface events in a 100 g silicon cryogenic dark matter detector. Surface events, calibrated using a 14C electron source, were found to have faster rise times (∼5 μs) than bulk gamma and neutron events (∼7 μs). Using this effect, we were able to discriminate bulk nuclear recoil events from a surface electron background at better than the 97% level above 25 keV recoil energy. The phonon risetime for bulk gamma events was dependent on the applied voltage, confirming that phonons produced from electron-hole emission are ballistic.

We have demonstrated the use of superconducting transition edge sensors for the wide-band detection of individual photons from the mid infrared (IR), through the optical, and into the far ultraviolet (UV). These tungsten transition edge sensors are squares about 18 μm on a side and detect single photon events above a threshold of 0.3 eV (4 μm wavelength), with an energy resolution of 0.15 eV full width at half maximum, and with a risetime (falltime) of .5 μs (60 μs). The calibration data extend up to the UV cutoff of the fiber optic feed at 3.5 eV (350 nm).

We have demonstrated a new type of phonon sensor for cryogenic particle detectors with a high-bandwidth SQUID readout. Our Quasiparticle trapping assisted Electrothermal feedback Transition edge sensor (QET) utilizes aluminum quasiparticle traps attached to a tungsten superconducting transition edge sensor patterned on a silicon substrate. The tungsten lines are voltage biased and self-regulate in the transition region. We have tested three versions of these detectors. One detector consisted of four QET sensors patterned on the surface of a 1 cm × 1 cm × 1 mm silicon substrate. With this detector, we have shown an energy resolution of ∼400 eV FWHM and position sensitivity of ∼0.3 mm for 6 keV X-rays from an 55 Fe source. We tested a second detector identical to the first but with the addition of an ionization sensor. With information from the ionization channel, we were able to distinguish electron-recoil events from nuclear-recoil events. Most recently, we have tested a 2 cm × 2 cm × 2 mm detector with four QET sensors.

Using improved Ge and Si detectors, better neutron shielding, and increased counting time, the Cryogenic Dark Matter Search (CDMS) experiment has obtained stricter limits on the cross section of weakly interacting massive particles (WIMPs) elastically scattering from nuclei. Increased discrimination against electromagnetic backgrounds and reduction of neutron flux confirm WIMP-candidate events previously detected by CDMS were consistent with neutrons and give limits on spin-independent WIMP interactions which are >2X lower than previous CDMS results for high WIMP mass, and which exclude new parameter space for WIMPs with mass between 8-20 GeV/c^2., 4 pages, 4 figures

The Cryogenic Dark Matter Search (CDMS) uses Ge and Si detectors to search for Weakly Interacting Massive Particles (WIMPs) via their elastic-scattering interaction with atomic nuclei. The present results from CDMS give limits on the spin-independent WIMP-nucleon elastic-scattering cross section that exclude previously unexplored parameter space above 10 GeV/c2. The second phase of the CDMS experiment, scheduled to start in January 2002, is expected to improve on the present sensitivity by more than two orders of magnitude.

CD4(+)CD25(+) suppressor T (TS) cells play a critical role in the maintenance of peripheral tolerance. We examined here proliferative and functional responses as well as differential gene expression in T(S) cells. We found that T(S) cells were hyporesponsive to antigenic stimuli in vivo and unable to flux Ca(2+) upon T cell receptor (TCR) engagement. However, T(S) cells were not impaired in their proliferative response to lymphopenia, which was dependent on major histocompatibility complex class II expression. Homeostatic proliferation did not abolish T(S) cell anergy; rather, it substantially augmented T(S) cell function. DNA array analyses identified genes that may inhibit responsiveness at a number of levels in multiple signaling cascades in T(S) cells, as well as several anti-apoptotic genes that may mediate their survival.

In September 1999, the Cryogenic Dark Matter Search (CDMS) completed a nine month run with the first generation detectors (0.5 kg of germanium BLIPs sensing thermal phonons and ionization). The data acquired in this run significantly decrease the upper limits on WIMP interaction in germanium by a factor 2.5 to 10 depending on the mass region and begin to probe supersymmetry. The results are however strongly inconsistent with the claims of the DAMA experiment.

The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for weakly interacting massive particles (WIMPs) via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. CDMS data, accounting for the neutron background, give limits on the spin-independent WIMP-nucleon elastic-scattering cross section that exclude unexplored parameter space above 10 GeV c-2 WIMP mass and. at > 75% CL. the entire 3σ allowed region for the WIMP signal reported by the DAMA experiment.

TCR-self peptide:MHC interactions play a critical role in thymic positive selection, yet relatively little is known of their function in the periphery. It has been suggested that continued contact with selecting MHC molecules is necessary for long-term peripheral maintenance of naive T cells. More recent studies have also demonstrated a role for specific self peptide:MHC complexes in the homeostatic expansion of naive T cells in lymphopenic mice. Our examination of these processes revealed that, whereas self class II MHC molecules do have a modest effect on long-term survival of individual CD4+ T cells, interactions with specific TCR ligands are not required for peripheral naive CD4+ T cell maintenance. In contrast, selective engagement of TCRs by self-peptide:MHC complexes does promote proliferation of CD4+ T cells under severe lymphopenic conditions, and this division is associated with an activation marker phenotype that is different from that induced by antigenic stimulation. Importantly, however, the ability of naive T cells to divide in response to homeostatic stimuli does not appear to be stringently dependent on TCR-self peptide:MHC interactions. Therefore, these results show that the factors regulating survival and homeostatic expansion of naive T cells in the periphery are not identical. In addition, we provide evidence for a novel form of T cell proliferation that can occur independently of TCR signaling and suggest that this reflects another mechanism regulating homeostatic T cell expansion.

Control of virus infections and eradication of tumors usually involves the lytic activity of CD8+ cytotoxic T lymphocytes (CTLs). The induction of effective CTL immunity relies on several factors, one of the most important of which is CD4+ T cell help. Numerous studies have demonstrated the dependence of CTL priming on the presence of CD4+ T cells, but until recently little was known of the mechanisms regulating this process. Based on reports that CD4+ and CD8+ T cells must recognize antigen on the same antigen-presenting cell (APC), help was originally thought to be provided through the delivery of short-range, CD4+ T cell-secreted cytokines. However, the results of subsequent studies favor an alternative mechanism, whereby CD4+ T cells modify the APC, converting it into a stimulatory cell for CD8+ T cell priming. It is important that CD40 and its ligand, CD40L, have been implicated in the provision of this help and, in particular, the generation of long-lasting CTL memory. J. Leukoc. Biol. 67: 607–614; 2000.

The present report provides the first extensive characterization of the OT-I TCR transgenic line, which produces MHC class I-restricted, ovalbumin-specific, CD8+ T cells (OT-I cells). These cells are shown to be positively selected in vivo in H-2b C57BL/6 mice and in bm5 mice, which express the Kbm5 mutant molecule. In contrast, OT-I cells were not selected by mutant Kb molecules in bm1, bm3, bm8, bm10, bm11 or bm23 mice. Interestingly, however, when positive selection was examined in vitro in foetal thymic organ culture (FTOC), bm1 and bm8 were still poorly selective, but the bm3 haplotype now selected as efficiently as B6. The ability to select in vitro correlated with the capacity to present the ovalbumin (OVA) peptide to OT-I cells, as measured by induction of an OVA-specific proliferative response. These results suggest that a lower affinity TCR:MHC interaction may be necessary for positive selection in FTOC compared with selection in situ.

The Cryogenic Dark Matter Search (CDMS) employs low-temperature Ge and Si detectors to search for Weakly Interacting Massive Particles (WIMPs) via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. For recoil energies above 10 keV, events due to background photons are rejected with >99.9% efficiency, and surface events are rejected with >95% efficiency. The estimate of the background due to neutrons is based primarily on the observation of multiple-scatter events that should all be neutrons. Data selection is determined primarily by examining calibration data and vetoed events. Resulting efficiencies should be accurate to about 10%. Results of CDMS data from 1998 and 1999 with a relaxed fiducial-volume cut (resulting in 15.8 kg-days exposure on Ge) are consistent with an earlier analysis with a more restrictive fiducial-volume cut. Twenty-three WIMP candidate events are observed, but these events are consistent with a background from neutrons in all ways tested. Resulting limits on the spin-independent WIMP-nucleon elastic-scattering cross-section exclude unexplored parameter space for WIMPs with masses between 10-70 GeV c^{-2}. These limits border, but do not exclude, parameter space allowed by supersymmetry models and accelerator constraints. Results are compatible with some regions reported as allowed at 3-sigma by the annual-modulation measurement of the DAMA collaboration. However, under the assumptions of standard WIMP interactions and a standard halo, the results are incompatible with the DAMA most likely value at >99.9% CL, and are incompatible with the model-independent annual-modulation signal of DAMA at 99.99% CL in the asymptotic limit., 40 pages, 49 figures (4 in color), submitted to Phys. Rev. D; v.2:clarified conclusions, added content and references based on referee's and readers' comments; v.3: clarified introductory sections, added figure based on referee's comments

Our detectors are superconducting transition edge sensors (TESs) optimized for the wide band detection of individual photons from the mid infrared, through the optical, and into the near ultraviolet. We typically achieve an energy resolution of 0.15 eV FWHM over this range with timing resolution of 100 ns. We have measured photon events with sub- microsecond rise times and 3 microsecond fall times allowing count rates as high as 30 kHz without significant degradation in energy resolution. Such characteristics along with the predicted high quantum efficiency (10% in IR to 50% in optical-UV) make our TES detectors very appealing for low-flux applications which have energy and timing requirements, such as fast spectrophotometry for observational astronomy. We present results from our recent observation of the Crab Pulsar (PSR BO531 + 21) which demonstrate the ability of our sensors to extract wide band phase-resolved spectroscopic information of the pulsar using the student-class 24 inch telescope on the campus of Stanford University. We present a description of the optical system and an analysis of the single pixel energy response.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This paper reviews recent studies of mesoscopic fluctuations in transport through ballistic quantum dots, emphasizing differences between conduction through open dots and tunneling through nearly isolated dots. Both the open dots and the tunnel-contacted dots show random, repeatable conductance fluctuations with universal statistical proper-ties that are accurately characterized by a variety of theoretical models including random matrix theory, semiclassical methods and nonlinear sigma model calculations. We apply these results in open dots to extract the dephasing rate of electrons within the dot. In the tunneling regime, electron interaction dominates transport since the tunneling of a single electron onto a small dot may be sufficiently energetically costly (due to the small capacitance) that conduction is suppressed altogether. How interactions combine with quantum interference are best seen in this regime., 15 pages, 11 figures, PDF 2.1 format, to appear in "Chaos, Solitons & Fractals"

Despite the discovery of MACHO dark matter in our galactic halo, much of the inferred halo mass seems still to be missing [1]. If we assume that this missing mass is in the form of the weakly interacting massive particles (WIMPs) predicted by supersymmetry [2], then we expect to find a flux of 107/mx cm-2 in the solar neighborhood or 104-106 cm-2 assuming the most likely mass range mx ∽ 10 - 1000 GeV and standard models of the galactic halo. These WIMPs have a total cross section for scattering on a nucleon of no more than 10-41cm2, leading to total scattering rates below 0.1 kg-1 day-1 of target mass.

Ballistic conductance fluctuations were measured in a GaAs quantum dot as a function of shape distortion and magnetic field. Shape distortion provides a novel source of conductance fluctuations and creates an effective “ensemble of dots,” allowing statistics to be studied at fixed field. Continuous changes in fluctuation statistics due to breaking of time-reversal symmetry are seen about zero magnetic field. Throughout, conductance fluctuation distributions appear Gaussian. The power spectrum of shape fluctuations appears exponential over three decades.

Investigations of semiconductor quantum dot structures have been predominately conducted on lithographically defined 2-dimensional electron gas structures at milli-Kelvin temperatures. Intriguing observations such as electron wave effects, single electron charging effects and electron-electron interactions have been observed. Although this work continues to expand our understanding of 0-dimensionally confined systems, higher temperature operating devices are limited because current lithography techniques are limited to approximately 500A feature sizes. An alternative approach is the use of growth induced islanding in strained heteroepitaxial semiconductor systems to create 0-dimensional systems without using lithography. Whereas the milli-Kelvin experiments use mature growth and lithography techniques, the growth induced islanding approach is comparatively new and current efforts in this area are devoted to understanding and controlling the growth of these islands and simple optical and electronic characterization. In this paper we bring together our recent work in these two areas.

Recent experiments measuring both the statistical and spectral properties of ballistic conductance fluctuations in GaAs quantum dots are described. Shape distortion using a small “pin” gate provides a novel means of generating conductance fluctuations, and also allows fluctuation statistics to be measured at fixed magnetic field. Changes in both the mean and the variance of conductance fluctuations are seen upon breaking time-reversal symmetry with an applied magnetic field. The phase-breaking time T φ(T) in the dot is measured using the power spectrum of conductance fluctuations and is compared to recent 0-D theory.

413 Background: Breast cancer is not a recognised malignant manifestation of Lynch Syndrome which includes colorectal, endometrial, gastric, ovarian and upper urinary tract tumours. In this study we report the prevalence of breast cancer in Irish Lynch Syndrome families and determine immunohistochemical expression of mismatch repair proteins (MMR) in available breast cancer tissue. Methods: Breast cancer prevalence was determined among Lynch Syndrome kindreds from two institutions in Ireland, and a genotype phenotype correlation was investigated. One kindred was omitted due to the presence of a biallelic MMR and BRCA1 mutation. The clinicopathological data that was collected on breast cancer cases included age of onset, morphology, and hormone receptor status. Immunohistochemical staining was performed for MLH1, MSH2, MSH6, and PMS2 on all available breast cancer tissue from affected individuals. Results: The distribution of MMR mutations seen in 16 pedigrees was as follows; MLH1 (n=5), MSH2 (7), MSH6 (3), PMS2 (1). Sixty cases of colorectal cancer and 14 cases of endometrial cancer were seen. Seven breast cancers (5 invasive ductal and 2 invasive lobular cancers) and 1 case of ductal carcinoma in situ were reported in 7 pedigrees. This compared with 4 cases of prostate cancer. Six MSH2 mutations and 1 MSH6 mutation were identified in the 7 Lynch syndrome kindreds. Median age of breast cancer diagnosis was 49 years (range 38-57). Hormone receptor status is available on 3 breast cancer cases at time of abstract submission; all were ER positive and HER 2 negative. All cases had grade 2 or 3 tumours. Final results of immunohistochemistry for mismatch repair protein expression on breast cancer samples are pending and will be reported at the meeting. One breast cancer has been tested to date and demonstrated loss of MSH2 protein expression in an individual carrying an MSH2 mutation. Conclusions: Breast cancer occurred at an early age and was more common than prostate cancer in Irish Lynch Syndrome pedigrees. All reported breast cancer cases were in kindreds with MSH2 or MSH6 mutations. Enhanced breast cancer screening may be warranted in certain Lynch Syndrome kindreds.