5,182 research outputs found
Violation of the I=1/2 rule in the nonmesonic weak decay of hypernuclei
Violations of the I=1/2 rule are investigated in the nonmesonic weak
hypernuclear decay using a weak NNN transition potential based on
meson exchange. While the weak I=3/2 matrix elements of baryons with
pseudoscalar mesons are known to be very small, the same matrix elements of
baryons with vector mesons, evaluated in the factorization approximation, are
found to be significant. Within the uncertainties of the factorization
approximation we find that the total rate increases by at most 6% lying within
the error bars of the more recent experimental result. The neutron- to
proton-induced rate, on the other hand, can change by up to a factor of two,
while the asymmetry parameter is strongly affected as well.Comment: 17 pages. Paper related to a contribution presented at the
International Conference on Hypernuclear and Strange Particle Physics
(HYP97). Submitted to Phys. Lett.
Design and Fabrication of Three-Dimensional Scaffolds for Tissue Engineering of Human Heart Valves
We developed a new fabrication technique for 3-dimensional scaffolds for tissue engineering of human heart valve tissue. A human aortic homograft was scanned with an X-ray computer tomograph. The data derived from the X-ray computed tomogram were processed by a computer-aided design program to reconstruct a human heart valve 3-dimensionally. Based on this stereolithographic model, a silicone valve model resembling a human aortic valve was generated. By taking advantage of the thermoplastic properties of polyglycolic acid as scaffold material, we molded a 3-dimensional scaffold for tissue engineering of human heart valves. The valve scaffold showed a deviation of only +/- 3-4% in height, length and inner diameter compared with the homograft. The newly developed technique allows fabricating custom-made, patient-specific polymeric cardiovascular scaffolds for tissue engineering without requiring any suture materials. Copyright (c) 2008 S. Karger AG, Base
Visualizing enzymatic and cellular activities during tissue morphogenesis using ex vivo twophoton FRET microscopy
Morphogenesis is a critical step in embryogenesis during which tissue/organ transforms into its functional shape. The drastic change in tissue morphology signifies active cellular reorganization and extraâcellular matrix remodeling. Enzymatic activity vital to this process, especially that of matrix metalloproteinase (MMP), attracts a lot of research interests but proves difficult to
investigate using traditional methods. Förster resonance energy transfer (FRET) has emerged as a powerful technique for investigating biochemical interaction, but its usefulness in live tissues has not been well established.
Here we use a genetically encoded FRET biosensor with ex vivo twoâphoton microscopy to demonstrate a clear increase in MT1âMMP activity at the tip of a growing feather bud, which coincides with increased cellular motion, sometimes across the epidermalâdermal border, and weakened laminin
structure in the basement membrane. Laminin and collagen III are newly synthesized at the tip, strengthening the newly formed structure. These events also exhibit spatioâtemporal correlation with increased Src activity observed using another genetically encoded FRET biosensor. Our ex vivo biochemistry approach provides insights into the spatial and temporal profile of enzyme activities, and together with traditional approaches, offers a comprehensive understanding of the morphogenetic process. Furthermore, it can readily lend itself to the studying of other biological processes, such as cancer metastasis, where
enzymatic activity plays a central role
Genomic patterns of malignant peripheral nerve sheath tumor (MPNST) evolution correlate with clinical outcome and are detectable in cell-free DNA
UNLABELLED: Malignant peripheral nerve sheath tumor (MPNST), an aggressive soft-tissue sarcoma, occurs in people with neurofibromatosis type 1 (NF1) and sporadically. Whole-genome and multiregional exome sequencing, transcriptomic, and methylation profiling of 95 tumor samples revealed the order of genomic events in tumor evolution. Following biallelic inactivation of NF1, loss of CDKN2A or TP53 with or without inactivation of polycomb repressive complex 2 (PRC2) leads to extensive somatic copy-number aberrations (SCNA). Distinct pathways of tumor evolution are associated with inactivation of PRC2 genes and H3K27 trimethylation (H3K27me3) status. Tumors with H3K27me3 loss evolve through extensive chromosomal losses followed by whole-genome doubling and chromosome 8 amplification, and show lower levels of immune cell infiltration. Retention of H3K27me3 leads to extensive genomic instability, but an immune cell-rich phenotype. Specific SCNAs detected in both tumor samples and cell-free DNA (cfDNA) act as a surrogate for H3K27me3 loss and immune infiltration, and predict prognosis.
SIGNIFICANCE: MPNST is the most common cause of death and morbidity for individuals with NF1, a relatively common tumor predisposition syndrome. Our results suggest that somatic copy-number and methylation profiling of tumor or cfDNA could serve as a biomarker for early diagnosis and to stratify patients into prognostic and treatment-related subgroups. This article is highlighted in the In This Issue feature, p. 517
An Investigation of Be/X-ray Pulsars with OGLE-III Data
We have studied five seasons of OGLE-III data for eight SMC Be/X-ray pulsars
for which no other survey data were available. We have determined orbital
periods for four of these binary systems, one of which also shows nonradial
pulsations. Optical identification of SMC X-2 is reconsidered, but no periods
were found for either of the two possible candidates
Culture in embryonic kidney serum and xeno-free media as renal cell carcinoma and renal cell carcinoma cancer stem cells research model
The use of fetal bovine serum hinders obtaining reproducible experimental results and should also be removed in hormone and growth factor studies. In particular hormones found in FBS act globally on cancer cell physiology and influence transcriptome and metabolome. The aim of our study was to develop a renal carcinoma serum free culture model optimized for (embryonal) renal cells in order to select the best study model for downstream auto-, para- or endocrine research. Secondary aim was to verify renal carcinoma stem cell culture for this application. In the study, we have cultured renal cell carcinoma primary tumour cell line (786-0) as well as human kidney cancer stem cells in standard 2D monolayer cultures in Roswell Park Memorial Institute Medium or Dulbeccoâs Modified Eagleâs Medium and Complete Human Kidney Cancer Stem Cell Medium, respectively. Serum-free, animal-component free Human Embryonic Kidney 293 media were tested. Our results revealed that xeno-free embryonal renal cells optimized culture media provide a useful tool in RCC cancer biology research and at the same time enable effective growth of RCC. We propose bio-mimic RCC cell culture model with specific serum-free and xeno-free medium that promote RCC cell viability
Poly-MTO, {(CH_3)_{0.92} Re O_3}_\infty, a Conducting Two-Dimensional Organometallic Oxide
Polymeric methyltrioxorhenium, {(CH_{3})_{0.92}ReO_{3}}_{\infty} (poly-MTO),
is the first member of a new class of organometallic hybrids which adopts the
structural pattern and physical properties of classical perovskites in two
dimensions (2D). We demonstrate how the electronic structure of poly-MTO can be
tailored by intercalation of organic donor molecules, such as
tetrathiafulvalene (TTF) or bis-(ethylendithio)-tetrathiafulvalene (BEDT-TTF),
and by the inorganic acceptor SbF. Integration of donor molecules leads to
a more insulating behavior of poly-MTO, whereas SbF insertion does not
cause any significant change in the resistivity. The resistivity data of pure
poly-MTO is remarkably well described by a two-dimensional electron system.
Below 38 K an unusual resistivity behavior, similar to that found in doped
cuprates, is observed: The resistivity initially increases approximately as
ln) before it changes into a dependence below 2 K.
As an explanation we suggest a crossover from purely two-dimensional
charge-carrier diffusion within the \{ReO\} planes at high
temperatures to three-dimensional diffusion at low temperatures in a
disorder-enhanced electron-electron interaction scenario (Altshuler-Aronov
correction). Furthermore, a linear positive magnetoresistance was found in the
insulating regime, which is caused by spatial localization of itinerant
electrons at some of the Re atoms, which formally adopt a electronic
configuration. X-ray diffraction, IR- and ESR-studies, temperature dependent
magnetization and specific heat measurements in various magnetic fields suggest
that the electronic structure of poly-MTO can safely be approximated by a
purely 2D conductor.Comment: 15 pages, 16 figures, 2 table
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