5,285 research outputs found
Kinase-independent function of RIP1, critical for mature T-cell survival and proliferation.
The death receptor, Fas, triggers apoptotic death and is essential for maintaining homeostasis in the peripheral lymphoid organs. RIP1 was originally cloned when searching for Fas-binding proteins and was later shown to associate also with the signaling complex of TNFR1. Although Fas exclusively induces apoptosis, TNFR1 primarily activates the pro-survival/pro-inflammatory NF-κB pathway. Mutations in Fas lead to lymphoproliferative (lpr) diseases, and deletion of TNFR1 results in defective innate immune responses. However, the function of RIP1 in the adult lymphoid system has not been well understood, primarily owing to perinatal lethality in mice lacking the entire RIP1 protein in germ cells. This current study investigated the requirement for RIP1 in the T lineage using viable RIP1 mutant mice containing a conditional and kinase-dead RIP1 allele. Disabling the kinase activity of RIP1 had no obvious impact on the T-cell compartment. However, T-cell-specific deletion of RIP1 led to a severe T-lymphopenic condition, owing to a dramatically reduced mature T-cell pool in the periphery. Interestingly, the immature T-cell compartment in the thymus appeared intact. Further analysis showed that mature RIP1(-/-) T cells were severely defective in antigen receptor-induced proliferative responses. Moreover, the RIP1(-/-) T cells displayed greatly increased death and contained elevated caspase activities, an indication of apoptosis. In total, these results revealed a novel, kinase-independent function of RIP1, which is essential for not only promoting TCR-induced proliferative responses but also in blocking apoptosis in mature T cells
Probing Solar Convection
In the solar convection zone acoustic waves are scattered by turbulent sound
speed fluctuations. In this paper the scattering of waves by convective cells
is treated using Rytov's technique. Particular care is taken to include
diffraction effects which are important especially for high-degree modes that
are confined to the surface layers of the Sun. The scattering leads to damping
of the waves and causes a phase shift. Damping manifests itself in the width of
the spectral peak of p-mode eigenfrequencies. The contribution of scattering to
the line widths is estimated and the sensitivity of the results on the assumed
spectrum of the turbulence is studied. Finally the theoretical predictions are
compared with recently measured line widths of high-degree modes.Comment: 26 pages, 7 figures, accepted by MNRA
Emergency escape system uses self-braking mechanism on fixed cable
Slide-wire system with a twist level slide device incorporates automatic descent and braking for the safe and rapid evacuation of personnel from tall structures. This device is used on any tall structure that might require emergency evacuation. It is also used to transfer materials and equipment
Quantum Stochastic Processes and the Modelling of Quantum Noise
This brief article gives an overview of quantum mechanics as a {\em quantum
probability theory}. It begins with a review of the basic operator-algebraic
elements that connect probability theory with quantum probability theory. Then
quantum stochastic processes is formulated as a generalization of stochastic
processes within the framework of quantum probability theory. Quantum Markov
models from quantum optics are used to explicitly illustrate the underlying
abstract concepts and their connections to the quantum regression theorem from
quantum optics.Comment: 14 pages, invited article for the second edition of Springer's
Encyclopedia of Systems and Control (to appear). Comments welcom
Contemplations on Dirac's equation in quaternionic coordinates
A formulation of Dirac's equation using complex-quaternionic coordinates
appears to yield an enormous gain in formal elegance, as there is no longer any
need to invoke Dirac matrices. This formulation, however, entails several
peculiarities, which we investigate and attempt to interpret
Determining solar abundances using helioseismology
The recent downward revision of solar photospheric abundances of Oxygen and
other heavy elements has resulted in serious discrepancies between solar models
and solar structure as determined through helioseismology. In this work we
investigate the possibility of determining the solar heavy-element abundance
without reference to spectroscopy by using helioseismic data. Using the
dimensionless sound-speed derivative in the solar convection zone, we find that
the heavy element abundance, Z, of 0.0172 +/- 0.002, which is closer to the
older, higher value of the abundances.Comment: To appear in Ap
Thermonuclear Burning on the Accreting X-Ray Pulsar GRO J1744-28
We investigate the thermal stability of nuclear burning on the accreting
X-ray pulsar GRO J1744-28. The neutron star's dipolar magnetic field is
<3\times 10^{11} G if persistent spin-up implies that the magnetospheric radius
is less than the co-rotation radius. After inferring the properties of the
neutron star, we study the thermal stability of hydrogen/helium burning and
show that thermonuclear instabilities are unlikely causes of the hourly bursts
seen at very high accretion rates. We then discuss how the stability of the
thermonuclear burning depends on both the global accretion rate and the neutron
star's magnetic field strength. We emphasize that the appearance of the
instability (i.e., whether it looks like a Type I X-ray burst or a flare
lasting a few minutes) will yield crucial information on the neutron star's
surface magnetic field and the role of magnetic fields in convection. We
suggest that a thermal instability in the accretion disk is the origin of the
long (~300 days) outburst and that the recurrence time of these outbursts is
>50 years. We also discuss the nature of the binary and point out that a
velocity measurement of the stellar companion (most likely a Roche-lobe filling
giant with m_K>17) will constrain the neutron star mass.Comment: 19 pages, 3 PostScript figures, uses aaspp4.sty and epsfig.sty, to
appear in the Astrophysical Journa
Probing the internal magnetic field of slowly pulsating B-stars through g modes
We suggest that high-order g modes can be used as a probe of the internal
magnetic field of SPB (slowly pulsating B) stars. The idea is based on earlier
work by the authors which analytically investigated the effect of a vertical
magnetic field on p and g modes in a plane-parallel isothermal stratified
atmosphere. It was found that even a weak field can significantly shift the
g-mode frequencies -- the effect increases with mode order. In the present
study we adopt the classical perturbative approach to estimate the internal
field of a 4 solar mass SPB star by looking at its effect on a low-degree
() and high-order () g mode with a period of about 1.5 d. We find
that a polar field strength of about 110 kG on the edge of the convective core
is required to produce a frequency shift of 1%. Frequency splittings of that
order have been observed in several SPB variables, in some cases clearly too
small to be ascribed to rotation. We suggest that they may be due to a poloidal
field with a strength of order 100 kG, buried in the deep interior of the star.Comment: 4 pages, 2 figures (to appear in Astronomy & Astrophysics
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