363 research outputs found
Stochastic Model and Equivalent Ferromagnetic Spin Chain with Alternation
We investigate a non-equilibrium reaction-diffusion model and equivalent
ferromagnetic spin 1/2 XY spin chain with alternating coupling constant. The
exact energy spectrum and the n-point hole correlations are considered with the
help of the Jordan-Wigner fermionization and the inter-particle distribution
function method. Although the Hamiltonian has no explicit translational
symmetry, the translational invariance is recovered after long time due to the
diffusion. We see the scaling relations for the concentration and the two-point
function in finite size analysis.Comment: 7 pages, LaTeX file, to appear in J. Phys. A: Math. and Ge
Mature seed-derived callus of the model indica rice variety Kasalath is highly competent in Agrobacterium-mediated transformation
We previously established an efficient Agrobacterium-mediated transformation system using primary calli derived from mature seeds of the model japonica rice variety Nipponbare. We expected that the shortened tissue culture period would reduce callus browningāa common problem with the indica transformation system during prolonged tissue culture in the undifferentiated state. In this study, we successfully applied our efficient transformation system to Kasalathāa model variety of indica rice. The Luc reporter system is sensitive enough to allow quantitative analysis of the competency of rice callus for Agrobacterium-mediated transformation. We unexpectedly discovered that primary callus of Kasalath exhibits a remarkably high competency for Agrobacterium-mediated transformation compared to Nipponbare. Southern blot analysis and Luc luminescence showed that independent transformation events in primary callus of Kasalath occurred successfully at ca. tenfold higher frequency than in Nipponbare, and single copy T-DNA integration was observed in ~40% of these events. We also compared the competency of secondary callus of Nipponbare and Kasalath and again found superior competency in Kasalath, although the identification and subsequent observation of independent transformation events in secondary callus is difficult due to the vigorous growth of both transformed and non-transformed cells. An efficient transformation system in Kasalath could facilitate the identification of QTL genes, since many QTL genes are analyzed in a NipponbareĀ ĆĀ Kasalath genetic background. The higher transformation competency of Kasalath could be a useful trait in the establishment of highly efficient systems involving new transformation technologies such as gene targeting
Molecular structural order and anomalies in liquid silica
The present investigation examines the relationship between structural order,
diffusivity anomalies, and density anomalies in liquid silica by means of
molecular dynamics simulations. We use previously defined orientational and
translational order parameters to quantify local structural order in atomic
configurations. Extensive simulations are performed at different state points
to measure structural order, diffusivity, and thermodynamic properties. It is
found that silica shares many trends recently reported for water [J. R.
Errington and P. G. Debenedetti, Nature 409, 318 (2001)]. At intermediate
densities, the distribution of local orientational order is bimodal. At fixed
temperature, order parameter extrema occur upon compression: a maximum in
orientational order followed by a minimum in translational order. Unlike water,
however, silica's translational order parameter minimum is broad, and there is
no range of thermodynamic conditions where both parameters are strictly
coupled. Furthermore, the temperature-density regime where both structural
order parameters decrease upon isothermal compression (the structurally
anomalous regime) does not encompass the region of diffusivity anomalies, as
was the case for water.Comment: 30 pages, 8 figure
Generic mechanism for generating a liquid-liquid phase transition
Recent experimental results indicate that phosphorus, a single-component
system, can have two liquid phases: a high-density liquid (HDL) and a
low-density liquid (LDL) phase. A first-order transition between two liquids of
different densities is consistent with experimental data for a variety of
materials, including single-component systems such as water, silica and carbon.
Molecular dynamics simulations of very specific models for supercooled water,
liquid carbon and supercooled silica, predict a LDL-HDL critical point, but a
coherent and general interpretation of the LDL-HDL transition is lacking. Here
we show that the presence of a LDL and a HDL can be directly related to an
interaction potential with an attractive part and two characteristic
short-range repulsive distances. This kind of interaction is common to other
single-component materials in the liquid state (in particular liquid metals),
and such potentials are often used to decribe systems that exhibit a density
anomaly. However, our results show that the LDL and HDL phases can occur in
systems with no density anomaly. Our results therefore present an experimental
challenge to uncover a liquid-liquid transition in systems like liquid metals,
regardless of the presence of the density anomaly.Comment: 5 pages, 3 ps Fig
Intra-molecular coupling as a mechanism for a liquid-liquid phase transition
We study a model for water with a tunable intra-molecular interaction
, using mean field theory and off-lattice Monte Carlo simulations.
For all , the model displays a temperature of maximum
density.For a finite intra-molecular interaction ,our
calculations support the presence of a liquid-liquid phase transition with a
possible liquid-liquid critical point for water, likely pre-empted by
inevitable freezing. For J=0 the liquid-liquid critical point disappears at
T=0.Comment: 8 pages, 4 figure
Basonuclin-Null Mutation Impairs Homeostasis and Wound Repair in Mouse Corneal Epithelium
At least two cellular processes are required for corneal epithelium homeostasis and wound repair: cell proliferation and cell-cell adhesion. These processes are delicately balanced to ensure the maintenance of normal epithelial function. During wound healing, these processes must be reprogrammed in coordination to achieve a rapid re-epithelialization. Basonuclin (Bnc1) is a cell-type-specific transcription factor expressed mainly in the proliferative keratinocytes of stratified epithelium (e.g., corneal epithelium, epidermis and esophageal epithelium) and the gametogenic cells in testis and ovary. Our previous work suggested that basonuclin could regulate transcription of ribosomal RNA genes (rDNA) and genes involved in chromatin structure, transcription regulation, cell-cell junction/communication, ion-channels and intracelllular transportation. However, basonuclin's role in keratinocytes has not been demonstrated in vivo. Here we show that basonuclin-null mutation disrupts corneal epithelium homeostasis and delays wound healing by impairing cell proliferation. In basonuclin-null cornea epithelium, RNA polymerase I (Pol I) transcription is perturbed. This perturbation is unique because it affects transcripts from a subset of rDNA. Basonuclin-null mutation also perturbs RNA polymerase II (Pol II) transcripts from genes encoding chromatin structure proteins histone 3 and HMG2, transcription factor Gli2, gap-junction protein connexin 43 and adheren E-cadherin. In most cases, a concerted change in mRNA and protein level is observed. However, for E-cadherin, despite a notable increase in its mRNA level, its protein level was reduced. In conclusion, our study establishes basonuclin as a regulator of corneal epithelium homeostasis and maintenance. Basonuclin likely coordinates functions of a subset of ribosomal RNA genes (rDNA) and a group of protein coding genes in cellular processes critical for the regulation of cell proliferation
Transperitoneal laparoscopic right radical nephrectomy for renal cell carcinoma and end-stage renal disease: a case report
Nephron-sparing surgery (partial nephrectomy) results are similar to those of radical nephrectomy for small (<4 cm) renal tumors. However, in patients with end-stage renal disease, radical nephrectomy emerges as a more efficient treatment for localized renal cell cancer. Laparoscopic radical nephrectomy (LRN) increasingly is being performed. The objective of the present study was to present a case of a patient under hemodialysis who was submitted to LRN for a small renal mass and discuss the current issues concerning this approach. It appears that radical nephrectomy should be the standard treatment in dialysis patients even for small tumors. The laparoscopic technique is associated with acceptable cancer-specific survival and recurrence rate along with shorter hospital stay, less postoperative pain and earlier return to normal activities
Long-Time Tails and Anomalous Slowing Down in the Relaxation of Spatially Inhomogeneous Excitations in Quantum Spin Chains
Exact analytic calculations in spin-1/2 XY chains, show the presence of
long-time tails in the asymptotic dynamics of spatially inhomogeneous
excitations. The decay of inhomogeneities, for , is given in the
form of a power law where the relaxation time
and the exponent depend on the wave vector ,
characterizing the spatial modulation of the initial excitation. We consider
several variants of the XY model (dimerized, with staggered magnetic field,
with bond alternation, and with isotropic and uniform interactions), that are
grouped into two families, whether the energy spectrum has a gap or not. Once
the initial condition is given, the non-equilibrium problem for the
magnetization is solved in closed form, without any other assumption. The
long-time behavior for can be obtained systematically in a form
of an asymptotic series through the stationary phase method. We found that
gapped models show critical behavior with respect to , in the sense that
there exist critical values , where the relaxation time
diverges and the exponent changes discontinuously. At those points, a
slowing down of the relaxation process is induced, similarly to phenomena
occurring near phase transitions. Long-lived excitations are identified as
incommensurate spin density waves that emerge in systems undergoing the Peierls
transition. In contrast, gapless models do not present the above anomalies as a
function of the wave vector .Comment: 25 pages, 2 postscript figures. Manuscript submitted to Physical
Review
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