3,555 research outputs found
Reconnection of superfluid vortex bundles
Using the vortex filament model and the Gross Pitaevskii nonlinear
Schroedinger equation, we show that bundles of quantised vortex lines in helium
II are structurally robust and can reconnect with each other maintaining their
identity. We discuss vortex stretching in superfluid turbulence and show that,
during the bundle reconnection process, Kelvin waves of large amplitude are
generated, in agreement with the finding that helicity is produced by nearly
singular vortex interactions in classical Euler flows.Comment: 10 pages, 7 figure
Evaporation of a packet of quantized vorticity
A recent experiment has confirmed the existence of quantized turbulence in
superfluid He3-B and suggested that turbulence is inhomogenous and spreads away
from the region around the vibrating wire where it is created. To interpret the
experiment we study numerically the diffusion of a packet of quantized vortex
lines which is initially confined inside a small region of space. We find that
reconnections fragment the packet into a gas of small vortex loops which fly
away. We determine the time scale of the process and find that it is in order
of magnitude agreement with the experiment.Comment: figure 1a,b,c and d, figure2, figure
Characterization of Borrelia Burgdorferi BlyA and BlyB Proteins: a Prophage-Encoded Holin-Like System
The conserved cp32 plasmid family of Borrelia burgdorferi was recently shown to be packaged into a bacteriophage particle (C. H. Eggers and D. S. Samuels, J. Bacteriol. 181:7308-7313, 1999), This plasmid encodes BlyA, a 7.4-kDa membrane-interactive protein, and BlyB, an accessory protein, which were previously proposed to comprise a hemolysis system. Our genetic and biochemical evidence suggests that this hypothesis is incorrect and that BlyA and BlyB function instead as a prophage-encoded holin or holin-like system for this newly described bacteriophage, An Escherichia coli mutant containing the blyAB locus that was defective for the normally cryptic host hemolysin SheA was found to be nonhemolytic, suggesting that induction of sheA by blyAB expression was responsible for the hemolytic activity observed previously, Analysis of the structural features of BlyA indicated greater structural similarity to bacteriophage-encoded holins than to hemolysins, Consistent with holin characteristics, subcellular localization studies with E. coli and B. burgdorferi indicated that BlyA is solely membrane associated and that BlyB is a soluble protein. Furthermore, BlyA exhibited a holin-like function by promoting the endolysin-dependent lysis of an induced lambda lysogen that was defective in the holin gene. Finally, induction of the cp32 prophage in B. burgdorferi dramatically stimulated blyAB expression. Our results provide the first evidence of a prophage-encoded holin within Borrelia
Medullary thyroid cancer in a 9-week-old infant with familial MEN 2B: Implications for timing of prophylactic thyroidectomy
BACKGROUND: Patients with Multiple Endocrine Neoplasia type 2 (MEN 2) are at high risk of developing aggressive medullary thyroid carcinoma (MTC) in childhood, with the highest risk in those with MEN type 2B (of whom >95% have an M918T RET proto-oncogene mutation). Metastatic MTC has been reported as young as 3 months of age. Current guidelines recommend prophylactic thyroidectomy within the first year of life for MEN 2B. PATIENT FINDINGS: We report a 9-week-old infant with MTC due to familial MEN 2B. A full-term male infant, born to a mother with known MEN 2B and metastatic MTC, had an M918T RET proto-oncogene mutation confirmed at 4 weeks of age. He underwent prophylactic total thyroidectomy at 9 weeks of age. Pathology showed a focal calcitonin-positive nodule (2.5 mm), consistent with microscopic MTC. SUMMARY: This case highlights the importance of early prophylactic thyroidectomy in MEN 2B. Although current guidelines recommend surgery up to a year of life, MTC may occur in the first few weeks of life, raising the question of how early we should intervene. In this report, we discuss the risks, benefits and barriers to performing earlier thyroidectomy, soon after the first month of life, and make suggestions to facilitate timely intervention. Prenatal anticipatory surgical scheduling could be considered in familial MEN 2B. Multidisciplinary collaboration between adult and pediatric specialists is key to the optimal management of the infant at risk
What Brown saw and you can too
A discussion is given of Robert Brown's original observations of particles
ejected by pollen of the plant \textit{Clarkia pulchella} undergoing what is
now called Brownian motion. We consider the nature of those particles, and how
he misinterpreted the Airy disc of the smallest particles to be universal
organic building blocks. Relevant qualitative and quantitative investigations
with a modern microscope and with a "homemade" single lens microscope similar
to Brown's, are presented.Comment: 14.1 pages, 11 figures, to be published in the American Journal of
Physics. This differs from the previous version only in the web site referred
to in reference 3. Today, this Brownian motion web site was launched, and
http://physerver.hamilton.edu/Research/Brownian/index.html, is now correc
Polarization of superfluid turbulence
We show that normal fluid eddies in turbulent helium II polarize the tangle
of quantized vortex lines present in the flow, thus inducing superfluid
vorticity patterns similar to the driving normal fluid eddies. We also show
that the polarization is effective over the entire inertial range. The results
help explain the surprising analogies between classical and superfluid
turbulence which have been observed recently.Comment: 3 figure
Specific heat of the Kelvin modes in low temperature superfluid turbulence
It is pointed out that the specific heat of helical vortex line excitations,
in low temperature superfluid turbulence experiments carried out in helium II,
can be of the same order as the specific heat of the phononic quasiparticles.
The ratio of Kelvin mode and phonon specific heats scales with L_0 T^{-5/2},
where L_0 represents the smoothed line length per volume within the vortex
tangle, such that the contribution of the vortex mode specific heat should be
observable for L_0 = 10^6-10^8 cm^{-2}, and at temperatures which are of order
1-10 mK.Comment: 3 pages, 1 figur
Transduction by Phi Bb-1, a Bacteriophage of Borrelia Burgdorferi
We previously described a bacteriophage of the Lyme disease agent Borrelia burgdorferi designated phi BB-1. This phage packages the host complement of the 32-kb circular plasmids (cp32s), a group of homologous molecules found throughout the genus Borrelia. To demonstrate the ability of phi BB-1 to package and transduce DNA, a kanamycin resistance cassette was inserted into a cloned fragment of phage DNA, and the resulting construct was transformed into B. burgdorferi CA-11.2A cells. The kan cassette recombined into a resident cp32 and was stably maintained. The cp32 containing the kan cassette was packaged by phi BB-1 released from this B. burgdorferi strain. phi BB-1 has been used to transduce this antibiotic resistance marker into naive CA-11.2A cells, as well as two other strains of B. burgdorferi. This is the first direct evidence of a mechanism for lateral gene transfer in B. burgdorferi
Circadian and dark-pulse activation of orexin/hypocretin neurons
Temporal control of brain and behavioral states emerges as a consequence of the interaction between circadian and homeostatic neural circuits. This interaction permits the daily rhythm of sleep and wake, regulated in parallel by circadian cues originating from the suprachiasmatic nuclei (SCN) and arousal-promoting signals arising from the orexin-containing neurons in the tuberal hypothalamus (TH). Intriguingly, the SCN circadian clock can be reset by arousal-promoting stimuli while activation of orexin/hypocretin neurons is believed to be under circadian control, suggesting the existence of a reciprocal relationship. Unfortunately, since orexin neurons are themselves activated by locomotor promoting cues, it is unclear how these two systems interact to regulate behavioral rhythms. Here mice were placed in conditions of constant light, which suppressed locomotor activity, but also revealed a highly pronounced circadian pattern in orexin neuronal activation. Significantly, activation of orexin neurons in the medial and lateral TH occurred prior to the onset of sustained wheel-running activity. Moreover, exposure to a 6 h dark pulse during the subjective day, a stimulus that promotes arousal and phase advances behavioral rhythms, activated neurons in the medial and lateral TH including those containing orexin. Concurrently, this stimulus suppressed SCN activity while activating cells in the median raphe. In contrast, dark pulse exposure during the subjective night did not reset SCN-controlled behavioral rhythms and caused a transient suppression of neuronal activation in the TH. Collectively these results demonstrate, for the first time, pronounced circadian control of orexin neuron activation and implicate recruitment of orexin cells in dark pulse resetting of the SCN circadian clock
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