882 research outputs found
A perpetual switching system in pulmonary capillaries
Of the 300 billion capillaries in the human lung, a small fraction meet normal oxygen requirements at rest, with the remainder forming a large reserve. The maximum oxygen demands of the acute stress response require that the reserve capillaries are rapidly recruited. To remain primed for emergencies, the normal cardiac output must be parceled throughout the capillary bed to maintain low opening pressures. The flow-distributing system requires complex switching. Because the pulmonary microcirculation contains contractile machinery, one hypothesis posits an active switching system. The opposing hypothesis is based on passive switching that requires no regulation. Both hypotheses were tested ex vivo in canine lung lobes. The lobes were perfused first with autologous blood, and capillary switching patterns were recorded by videomicroscopy. Next, the vasculature of the lobes was saline flushed, fixed by glutaraldehyde perfusion, flushed again, and then reperfused with the original, unfixed blood. Flow patterns through the same capillaries were recorded again. The 16-min-long videos were divided into 4-s increments. Each capillary segment was recorded as being perfused if at least one red blood cell crossed the entire segment. Otherwise it was recorded as unperfused. These binary measurements were made manually for each segment during every 4 s throughout the 16-min recordings of the fresh and fixed capillaries (>60,000 measurements). Unexpectedly, the switching patterns did not change after fixation. We conclude that the pulmonary capillaries can remain primed for emergencies without requiring regulation: no detectors, no feedback loops, and no effectors-a rare system in biology. NEW & NOTEWORTHY The fluctuating flow patterns of red blood cells within the pulmonary capillary networks have been assumed to be actively controlled within the pulmonary microcirculation. Here we show that the capillary flow switching patterns in the same network are the same whether the lungs are fresh or fixed. This unexpected observation can be successfully explained by a new model of pulmonary capillary flow based on chaos theory and fractal mathematics
The orbital debris detector consortium: Suppliers of instruments for in-situ measurements of small-particles in the space environment
Industry and university participants have joined together to form the IMPA:Ct consortium (In-situ Monitors of the Particulate Ambient: Circumterrestrial) which offers a broad range of flight qualified instruments for monitoring the small particle (0.1 micron to 10 cm) environment in space. Instruments are available in 12 months or less at costs ranging from 0.5 to 1.5 million dollars (US) for the total program. Detector technologies represented by these groups are: impact-induced capacitor-discharge (MOS, metal-oxide-silicon), cratering or penetration of electroactive thin film (polyvinylidene fluoride (PVDF)), impact-plasma detection, acoustic detection, CCD tracking of optical scatter of sunlight, and photodiode detection of optical scatter of laser light. The operational characteristics, general spacecraft interface and resource requirements (mass/power/telemetry), cost and delivery schedules, and points of contact for seven different instruments are presented
Signals for CPT and Lorentz Violation in Neutral-Meson Oscillations
Experimental signals for indirect CPT violation in the neutral-meson systems
are studied in the context of a general CPT- and Lorentz-violating
standard-model extension. In this explicit theory, some CPT observables depend
on the meson momentum and exhibit diurnal variations. The consequences for CPT
tests vary significantly with the specific experimental scenario. The wide
range of possible effects is illustrated for two types of CPT experiment
presently underway, one involving boosted uncorrelated kaons and the other
involving unboosted correlated kaon pairs.Comment: Accepted in Physical Review D, scheduled for December 1999 issu
On the rate of quantum ergodicity in Euclidean billiards
For a large class of quantized ergodic flows the quantum ergodicity theorem
due to Shnirelman, Zelditch, Colin de Verdi\`ere and others states that almost
all eigenfunctions become equidistributed in the semiclassical limit. In this
work we first give a short introduction to the formulation of the quantum
ergodicity theorem for general observables in terms of pseudodifferential
operators and show that it is equivalent to the semiclassical eigenfunction
hypothesis for the Wigner function in the case of ergodic systems. Of great
importance is the rate by which the quantum mechanical expectation values of an
observable tend to their mean value. This is studied numerically for three
Euclidean billiards (stadium, cosine and cardioid billiard) using up to 6000
eigenfunctions. We find that in configuration space the rate of quantum
ergodicity is strongly influenced by localized eigenfunctions like bouncing
ball modes or scarred eigenfunctions. We give a detailed discussion and
explanation of these effects using a simple but powerful model. For the rate of
quantum ergodicity in momentum space we observe a slower decay. We also study
the suitably normalized fluctuations of the expectation values around their
mean, and find good agreement with a Gaussian distribution.Comment: 40 pages, LaTeX2e. This version does not contain any figures. A
version with all figures can be obtained from
http://www.physik.uni-ulm.de/theo/qc/ (File:
http://www.physik.uni-ulm.de/theo/qc/ulm-tp/tp97-8.ps.gz) In case of any
problems contact Arnd B\"acker (e-mail: [email protected]) or Roman
Schubert (e-mail: [email protected]
Chaotic eigenfunctions in momentum space
We study eigenstates of chaotic billiards in the momentum representation and
propose the radially integrated momentum distribution as useful measure to
detect localization effects. For the momentum distribution, the radially
integrated momentum distribution, and the angular integrated momentum
distribution explicit formulae in terms of the normal derivative along the
billiard boundary are derived. We present a detailed numerical study for the
stadium and the cardioid billiard, which shows in several cases that the
radially integrated momentum distribution is a good indicator of localized
eigenstates, such as scars, or bouncing ball modes. We also find examples,
where the localization is more strongly pronounced in position space than in
momentum space, which we discuss in detail. Finally applications and
generalizations are discussed.Comment: 30 pages. The figures are included in low resolution only. For a
version with figures in high resolution see
http://www.physik.uni-ulm.de/theo/qc/ulm-tp/tp99-2.htm
Genetic diversity of Brazilian isolates of feline immunodeficiency virus
We isolated Feline immunodeficiency virus (FIV) from three adult domestic cats, originating from two open shelters in Brazil. Viruses were isolated from PBMC following co-cultivation with the feline T-lymphoblastoid cell line MYA-1. All amplified env gene products were cloned directly into pGL8MYA. The nucleic acid sequences of seven clones were determined and then compared with those of previously described isolates. The sequences of all of the Brazilian virus clones were distinct and phylogenetic analysis revealed that all belong to subtype B. Three variants isolated from one cat and two variants were isolated from each of the two other cats, indicating that intrahost diversity has the potential to pose problems for the treatment and diagnosis of FIV infection
Increasing body mass index from age 5 to 14 years predicts asthma among adolescents: evidence from a birth cohort study
Background:Obesity and asthma are common disorders, and the prevalence of both has increased in recent decades. It has been suggested that increases in the prevalence of obesity might in part explain the increase in asthma prevalence. This study aims to examine the prospective association between change in body mass index (BMI) z-score between ages 5 and 14 years and asthma symptoms at 14 years. Methods:Data was taken from the Mater University Study of Pregnancy and its outcomes (MUSP), a birth cohort of 7223 mothers and children started in Brisbane (Australia) in 1981. BMI was measured at age 5 and 14 years. Asthma was assessed from maternal reports of symptoms at age 5 and 14 years. In this study analyses were conducted on 2911 participants who had information on BMI and asthma at both ages. Results: BMI z-score at age 14 and the change in BMI z-score from age 5 to 14–years were positively associated with asthma symptoms at age 14 years, whereas BMI z-score at age 5 was not associated with asthma at age 14. Adjustment for a range of early-life exposures did not substantially alter these findings. The association between change in BMI z-score with asthma symptoms at 14 years appeared stronger for male subjects compared with female subjects but there was no statistical evidence for a sex difference (P=0.36). Conclusions: Increase in BMI z-score between age 5 and 14 years is associated with increased risk of asthma symptoms in adolescence
First Neutrino Observations from the Sudbury Neutrino Observatory
The first neutrino observations from the Sudbury Neutrino Observatory are
presented from preliminary analyses. Based on energy, direction and location,
the data in the region of interest appear to be dominated by 8B solar
neutrinos, detected by the charged current reaction on deuterium and elastic
scattering from electrons, with very little background. Measurements of
radioactive backgrounds indicate that the measurement of all active neutrino
types via the neutral current reaction on deuterium will be possible with small
systematic uncertainties. Quantitative results for the fluxes observed with
these reactions will be provided when further calibrations have been completed.Comment: Latex, 7 pages, 10 figures, Invited paper at Neutrino 2000
Conference, Sudbury, Canada, June 16-21, 2000 to be published in the
Proceeding
Interferon-γ Activates Nuclear Factor-κ B in Oligodendrocytes through a Process Mediated by the Unfolded Protein Response
Our previous studies have demonstrated that the effects of the immune cytokine interferon-γ (IFN-γ) in immune-mediated demyelinating diseases are mediated, at least in part, by the unfolded protein response (UPR) in oligodendrocytes. Data indicate that some biological effects of IFN-γ are elicited through activation of the transcription factor nuclear factor-κB (NF-κB). Interestingly, it has been shown that activation of the pancreatic endoplasmic reticulum kinase (PERK) branch of the UPR triggers NF-κB activation. In this study, we showed that IFN-γ-induced NF-κB activation was associated with activation of PERK signaling in the oligodendroglial cell line Oli-neu. We further demonstrated that blockage of PERK signaling diminished IFN-γ-induced NF-κB activation in Oli-neu cells. Importantly, we showed that NF-κB activation in oligodendrocytes correlated with activation of PERK signaling in transgenic mice that ectopically express IFN-γ in the central nervous system (CNS), and that enhancing IFN-γ-induced activation of PERK signaling further increased NF-κB activation in oligodendrocytes. Additionally, we showed that suppression of the NF-κB pathway rendered Oli-neu cells susceptible to the cytotoxicity of IFN-γ, reactive oxygen species, and reactive nitrogen species. Our results indicate that the UPR is involved in IFN-γ-induced NF-κB activation in oligodendrocytes and suggest that NF-κB activation by IFN-γ represents one mechanism by which IFN-γ exerts its effects on oligodendrocytes in immune-mediated demyelinating diseases
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