554 research outputs found
Mediators of mechanotransduction between bone cells
Mechanical forces are known to regulate the function of tissues in the body, including bone. Bone adapts to its mechanical environment by altering its shape and increasing its size in response to increases in mechanical load associated with exercise, and by decreasing its size in response to decreases in mechanical load associated with microgravity or prolonged bed rest. Changes in bone size and shape are produced by a cooperative action of two main types of the bone cells - osteoclasts that destroy bone and osteoblasts that build bone. These cell types come from different developmental origins, and vary greatly in their characteristics, such as size, shape, and expression of receptor subtypes, which potentially may affect their responses to mechanical stimuli. The objective of this study is to compare the responses of osteoclasts and osteoblasts to mechanical stimulation.
This study has allowed us to conclude the following:
1. A mediator is released from a single source cell.
2. The response to the mediator changes with distance.
3. The value of the apparent diffusion coeficient increases with distance.
4. A plausible proposed mechanism is that ATP is released and degrades to ADP.
5. Future experiments are required to confim that ATP is the mediator as suggested
The earliest spectroscopy of the GRB 030329 afterglow with 6-m telescope
The earliest BTA (SAO RAS 6-m telescope) spectroscopic observations of the
GRB 030329 optical transient (OT) are presented, which almost coincide in time
with the "first break" ( day after the GRB) of the OT light curve.
The beginning of spectral changes are seen as early as hours after
the GRB. So, the onset of the spectral changes for day indicates that the
contribution from Type Ic supernova (SN) into the OT optical flux can be
detected earlier. The properties of early spectra of GRB 030329/SN 2003dh can
be consistent with a shock moving into a stellar wind formed from the pre-SN.
Such a behavior (similar to that near the UV shock breakout in SNe) can be
explained by the existence of a dense matter in the immediate surroundings of
massive stellar GRB/SN progenitor). The urgency is emphasized of observation of
early GRB/SN spectra for solving a question that is essential for understanding
GRB physical mechanism: {\it Do all} long-duration gamma-ray bursts are caused
by (or physically connected to) {\it ordinary} core-collapse supernovae? If
clear association of normal/ordinary core-collapse SNe (SN Ib/c, and others SN
types) and GRBs would be revealed in numbers of cases, we may have strong
observational limits for gamma-ray beaming and for real energetics of the GRB
sources.Comment: 4 pages, 5 figures. Proceedings of the 4th Workshop "Gamma-Ray Bursts
in the Afterglow Era", Roma, 2004 October 18-22, eds. L. Piro, L. Amati, S.
Covino, and B. Gendre. Il Nuovo Cimento, in pres
Kraichnan model of passive scalar advection
A simple model of a passive scalar quantity advected by a Gaussian
non-solenoidal ("compressible") velocity field is considered. Large order
asymptotes of quantum-field expansions are investigated by instanton approach.
The existence of finite convergence radius of the series is proved, a position
and a type of the corresponding singularity of the series in the regularization
parameter are determined. Anomalous exponents of the main contributions to the
structural functions are resummed using new information about the series
convergence and two known orders of the expansion.Comment: 21 page
The Multiband Photometry of GRB Host Galaxies: Comparison with the Spectral Energy Distributions of Nearby and Theoretical Modeling Galaxies
We present one of the results of photometry of the hosts of GRB for
the host galaxy of GRB 970508 and the theoretical modeling of its continuum
spectral energy distribution (SED) to show that it is important to take into
account internal extinction in the host galaxies. We compared the BVRI
broad-band flux spectrum of the host to template SEDs of local starburst
galaxies and found that there is a significant internal extintion in this host.
Moreover, this comparison allows us to derive the absolute magnitude
(M_{B_{rest}}) and rouhgly estimate reddening (A_V). Population synthesis
modeling of the continuum SED for different reddening laws demostrates that the
observational data of the host galaxy of GRB 970508 are best fitted by the
spectral properties of a model SED with extinction of A_V\approx 2.Comment: 3 pages, 2 figures, poster presentation on 2nd Rome Workshop on
Gamma-Ray Bursts in the Afterglow Er
Problems and prospects of development of ecological tourism in Ireland
The paper presents the research on the development of ecological tourism in Ireland. The basic directions and problems of development of ecotourism. Income from ecotourism in the country was analyzed in the article, as well as the model for the attraction of tourists to Irelan
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