42 research outputs found
Analysis of the generation of photon pairs in periodically poled lithium niobate
The process of spontaneous parametric down-conversion (SPDC) in nonlinear
crystals makes it fairly easy to generate entangled photon states. It has been
known for some time that the conversion efficiency can be improved by employing
quasi-phase-matching in periodically poled crystals. Using two single-photon
detectors, we have analyzed the photon pairs generated by SPDC in a
periodically poled lithium niobate crystal pumped by a femtosecond laser.
Several parameters could be varied in our setup, allowing us to obtain data in
close agreement with both thermal and Poissonian photon-pair distributions.Comment: 4 pages, 4 figures, uses ws-procs10x7.cls; v2: Sign in equation (5)
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Defective function of GABA-containing synaptic vesicles in mice lacking the AP-3B clathrin adaptor
AP-3 is a member of the adaptor protein (AP) complex family that regulates the vesicular transport of cargo proteins in the secretory and endocytic pathways. There are two isoforms of AP-3: the ubiquitously expressed AP-3A and the neuron-specific AP-3B. Although the physiological role of AP-3A has recently been elucidated, that of AP-3B remains unsolved. To address this question, we generated mice lacking μ3B, a subunit of AP-3B. μ3B−/− mice suffered from spontaneous epileptic seizures. Morphological abnormalities were observed at synapses in these mice. Biochemical studies demonstrated the impairment of γ-aminobutyric acid (GABA) release because of, at least in part, the reduction of vesicular GABA transporter in μ3B−/− mice. This facilitated the induction of long-term potentiation in the hippocampus and the abnormal propagation of neuronal excitability via the temporoammonic pathway. Thus, AP-3B plays a critical role in the normal formation and function of a subset of synaptic vesicles. This work adds a new aspect to the pathogenesis of epilepsy
Energetics of Nonthermal Electrons and Protons in Intense Solar Flares
Abstract We analyze Yohkoh gamma-ray energy spectra of X-class solar flares on October 27, 1991 (X6.1), November 6, 1997 (X9.4), July 14, 2000 (X5.7) and November 24, 2000 (X2.3) to study the energy content of nonthermal electrons and protons. The accelerated electron and proton spectra are derived from a spectral analysis of the continuum and lines above 1 MeV. The energy content in >1 MeV and >10 MeV protons are estimated to be 6x10 28 -4x10 30 and 2.5x10 28 -5x10 29 ergs, respectively. We study the flare to flare variation in the energy contents of > 1 MeV electrons and >10 MeV protons. Ratios of > 1 MeV electrons to >10 MeV proton energy contents vary within an order of magnitude
Role of multipotent fibroblasts in the healing colonic mucosa of rabbits. Ultrastructural and immunocytochemical study
Light- and electron microscopy and
immunocytochemistry were used to study the healing
colonic mucosa of rabbits after experimental excision.
Between 3 and 5 days, abundant young fibroblasts
which retained many features of mesenchymal cells
invaded the growing capillaries into the loose connective
tissue of the healing colonic mucosa. Our electron
microscopy revealed the transformation of these young
fibroblasts into smooth muscle cells, into histiocyte-like
cells involved in phagocytotic activity, and into
vasoformative cells incorporated into the growing
capillaries. The mitotic proliferation of pre-existing
smooth muscle cells at the ulcer margin did not seem to
be the major reason for re-establishment of the muscular
tissue.
The present immunocytochemistry revealed an active
production of fibronectin in rough endoplasmic
reticulum in the young fibroblasts. This may mean that
this glycoprotein is involved in the re-establishment of
both connective and muscular tissues by enhancement of
adhesion and chemoattractant activities of such cells. In
addition, the immunoreaction of endothelial celis of the
growing capillaries suggests a role of this glycoprotein
in the acceleration of the neocapillarization
Hyperplastic cellular components of a hemangiopericytoma. An ultrastructural study
Based on ultrastructural features of cellular
components of a hemangiopericytoma, hyperplastic cells
are classifiable into fibroblast-like (group 1), endotheloid
(group 11) and pericyte-like (group 111) cells. The
transformation of the group 1 cells to the group 11, or to
the group 111 cells, is pronounced in our electron
micrographs and this may imply that the group 1 cell is
the principal cell of origin in this neoplasm.
The smooth muscle-like (group IV) cells comprising
the media of the arteries and veins in this neoplasm may
represent modified, possibly de-differentiated smooth
muscle cells reacted to the neoplastic proliferation of the
surrounding adventitial (group 1) cells
The toxic effects of bis (tributyltin) oxide on the rat thoracic aorta
The toxic effects of bis (tributyltin) oxide
(TBTO) on the ultrastructure and permeability of rat
thoracic aorta were studied electron microscopically and
the accumulation sites of tin were determined with an
X-ray microanalyzer.
Male Wistar rats received O.O5ml/kg of TBTO as an
emulsion in 1 m1 of distilled water througb a stomach
tube. After time intervals of 2, 4, 6, 8, 10, 12 h after
intubation, thoracic aortae were isolated and prepared
for electron microscopy.
Marked swelling of mitochondria in the aortic
endothelial cells appeared at 4 h after TBTO treatment.
By x-ray microanalysis, tin L-a peaks (3.44 keV) were
obtained from these swollen mitochondria.
Subendothelial edema progressed between 6 and 8 h
after TBTO treatment. By tracer experiment, it was seen
that large amounts of peroxidase reaction products filled
the expanded subendothelial space. At 12 h after TBTO
treatment, degenerative changes of the endothelial cells
were prominent. These results indicated that orally
administered TBTO accumulated in the mitochondria of
the endothelial cells of thoracic aorta. The direct toxic
effects of TBTO on mitochondria might induce severe
damage to the endothelial cells and cause disturbance of
the permeability barrier function of the endothelial layer
and subendothelial edema