684 research outputs found

    The correlations between the spin frequencies and kHz QPOs of Neutron Stars in LMXBs

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    We studied the correlations between spin frequencies and kilohertz quasi-periodic oscillations (kHz QPOs) in neutron star low mass X-ray binaries. The updated data of kHz QPOs and spin frequencies are statistically analyzed. We found that when two simultaneous kHz QPOs are present in the power spectrum, the minimum frequency of upper kHz QPO is at least 1.3 times larger than the spin frequency, i.e. \nu_{s}<\nu_{2min}/1.3. We also found that the average kHz QPO peak separation in 6 Atoll sources anti-correlates with the spin frequency in the form \lan\dn\ran = -(0.19\pm0.05)\ns+(389.40\pm21.67)Hz. If we shifted this correlation in the direction of the peak separation by a factor of 1.5, this correlation matches the data points of the two accretion powered millisecond X-ray pulsars, SAX J1808.4-3658 and XTE J1807-294.Comment: 4 pages, 2 figures, accepted for publication in A&

    MAT-734: INCREASING THE DURABILITY AND RESILIENCE OF TALL BUILDINGS WITH PRECAST CONCRETE ENCLOSURE SYSTEMS

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    In this paper precast concrete wall systems are compared to curtain wall and window wall systems in terms of durability and disaster resilience of multi-story buildings. Window wall systems are currently the enclosure system of choice for tall residential buildings in most parts of North America. Precast concrete wall systems can be expected to last the lifetime of a building with routine seal replacement. These are highly durable systems. Windows within precast concrete wall systems will require replacement in 25-35 years but represent a limited portion of the wall area and hence are less costly and have less impact on building use interruption. The impact of façade choice on passive survivability and security are also considered. Maintaining livable temperatures in a space in Toronto, Ontario (a city with a climate similar to many Northern U.S. cities) during a power outage is shown to mostly depend on having little heat loss, reducing solar gains, and provision of thermal mass. A whole wall metric is also introduced which combines various vision and non-vision wall system heat loss components. A similar metric for solar gain is introduced. The most significant factor affecting this heat loss and solar gain (and thereby affecting thermal resilience) is to avoid high Window to Wall Ratios (WWR). This will apply for most wall systems but is most significant for systems like precast concrete where there is minimal thermal bridging through the insulation. In terms of security, precast concrete walls will protect occupants from projectiles and endure little damage during disasters. These impacts make precast concrete wall systems significantly more disaster resilient

    Coplanar waveguides on AlN for AlGaN/GaN MMIC applications

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    In this paper we present results on the characterization of Coplanar Waveguides (CPW) on AlN substrates. These transmission lines will be used in matching networks for high power Al- GaN/GaN ampliers. The large currents that will flow inside these ampliers require a large crosssectional conductor area resulting in CPW lines with large signal-to-ground spacings and/or large center conductor widths. The Line-Reflect-Line (LRL) algorithm was used in combination with a capacitance measurement to determine the transmission line parameters. It will be shown that the CPW lines with large dimensions show non-quasi- TEM behavior presumably related to parallel plate modes which influence decreases with sample thickness. The CPW lines show dispersion in the lowfrequency

    Polar decompositions of quaternion matrices in indefinite inner product spaces

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    Polar decompositions of quaternion matrices with respect to a given indefinite inner product are studied. Necessary and sufficient conditions for the existence of an HH-polar decomposition are found. In the process an equivalent to Witt's theorem on extending HH-isometries to HH-unitary matrices is given for quaternion matrices

    Timing properties and spectral states in Aquila X-1

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    We have analyzed five X-ray outbursts of the neutron-star soft X-ray transient Aql X-1 and investigated the timing properties of the source in correlation with its spectral states as defined by different positions in the color-color and hardness-intensity diagrams. The hard color and the source count rate serve as the distinguishing parameters giving rise to three spectral states: a low-intensity hard state, an intermediate state and a high-intensity soft state. These states are respectively identified with the extreme island, island and banana states that characterize the atoll sources. The large amount of data analyzed allowed us to perform for the first time a detailed timing analysis of the extreme island state. Differences in the aperiodic variability between the rise and the decay of the X-ray outbursts are found in this state: at the same place in the color-color diagram, during the rise the source exhibits more power at low frequencies (< 1 Hz), whereas during the decay the source is more variable at high frequencies (> 100 Hz). The very-low frequency noise that characterizes the banana-state power spectra below 1 Hz cannot be described in terms of a single power law but a two-component model is required. In two outbursts a new 6-10 Hz QPO has been discovered and tentatively identified with the normal/flaring branch-like oscillation observed only at the highest inferred mass accretion rates. We have compared the spectral and timing properties of Aql X-1 with those of other atoll and Z sources. Our results argue against a unification scheme for these two types of neutron-star X-ray binaries.Comment: 24 pages, 4 tables, 9 figures, accepted for publication in Ap

    UGT1A1*28 genotype and irinotecan dosage in patients with metastatic colorectal cancer: a Dutch Colorectal Cancer Group study

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    The aim of the study was to investigate the associations between UGT1A1*28 genotype and (1) response rates, (2) febrile neutropenia and (3) dose intensity in patients with metastatic colorectal cancer treated with irinotecan. UGT1A1*28 genotype was determined in 218 patients receiving irinotecan (either first-line therapy with capecitabine or second-line as monotherapy) for metastatic colorectal cancer. TA7 homozygotes receiving irinotecan combination therapy had a higher incidence of febrile neutropenia (18.2%) compared to the other genotypes (TA6/TA6 : 1.5%; TA6/TA7 : 6.5%, P=0.031). TA7 heterozygotes receiving irinotecan monotherapy also suffered more febrile neutropenia (19.4%) compared to TA6/TA6 genotype (2.2%; P=0.015). Response rates among genotypes were not different for both regimens: combination regimen, P=0.537; single-agent, P=0.595. TA7 homozygotes did not receive a lower median irinotecan dose, number of cycles (P-values ⩾0.25) or more frequent dose reductions compared to the other genotypes (P-values for trend; combination therapy: 0.62 and single-agent: 0.45). Reductions were mainly (>80%) owing to grade ⩾3 diarrhoea, not (febrile) neutropenia. TA7/TA7 patients have a higher incidence of febrile neutropenia upon irinotecan treatment, but were able to receive similar dose and number of cycles compared to other genotypes. Response rates were not significantly different

    Mean glucose during ICU admission is related to mortality by a U-shaped curve in surgical and medical patients: a retrospective cohort study

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    Lowering of hyperglycemia in the intensive care unit (ICU) is widely practiced. We investigated in which way glucose regulation, defined as mean glucose concentration during admission, is associated with ICU mortality in a medical and a surgical cohort. Retrospective database cohort study including patients admitted between January 2004 and December 2007 in a 20-bed medical/surgical ICU in a teaching hospital. Hyperglycemia was treated using a computerized algorithm targeting for glucose levels of 4.0-7.0 mmol/l. Five thousand eight hundred twenty-eight patients were eligible for analyses, of whom 1,339 patients had a medical and 4,489 had a surgical admission diagnosis. The cohorts were subdivided in quintiles of increasing mean glucose. We examined the relation between these mean glucose strata and mortality. In both cohorts we observed the highest mortality in the lowest and highest strata. Logistic regression analysis adjusted for age, sex, Acute Physiology and Chronic Health Evaluation II (APACHE II) score, admission duration and occurrence of severe hypoglycemia showed that in the medical cohort mean glucose levels 8.4 mmol/l and in the surgical cohort mean glucose levels 9.4 mmol/l were associated with significantly increased ICU mortality (OR 2.4-3.0 and 4.9-6.2, respectively). Limitations of the study were its retrospective design and possible incomplete correction for severity of disease. Mean overall glucose during ICU admission is related to mortality by a U-shaped curve in medical and surgical patients. In this cohort of patients a 'safe range' of mean glucose regulation might be defined approximately between 7.0 and 9.0 mmol/

    Simultaneous BeppoSAX and Rossi X-ray Timing Explorer observations of 4U1812-12

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    4U1812-12 is a faint persistent and weakly variable neutron star X-ray binary. It was observed by BeppoSAX between April 20th and 21st, 2000 in a hard spectral state with a bolometric luminosity of ~2x10^36 ergs/s. Its broad band energy spectrum is characterized by the presence of a hard X-ray tail extending above ~100 keV. It can be represented as the sum of a dominant hard Comptonized component (electron temperature of ~36 keV and optical depth ~3) and a weak soft component. The latter component which can be fitted with a blackbody of about 0.6 keV and equivalent radius of ~2 km is likely to originate from the neutron star surface. We also report on the first measurement of the power density spectrum of the source rapid X-ray variability, as recorded during a simultaneous snapshot observation performed by the Rossi X-ray Timing Explorer. As expected for a neutron star system in such hard spectral state, its power density spectrum is characterized by the presence of a ~0.7 Hz low frequency quasi-periodic oscillation together with three broad noise components, one of which extends above ~200 Hz.Comment: 6 pages, 3 figures, accepted for publication in A&
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