762 research outputs found
Nucleon-Nucleon interaction, charge symmetry breaking and renormalization
We study the interplay between charge symmetry breaking and renormalization
in the NN system for s-waves. We find a set of universality relations which
disentangle explicitly the known long distance dynamics from low energy
parameters and extend them to the Coulomb case. We analyze within such an
approach the One-Boson-Exchange potential and the theoretical conditions which
allow to relate the proton-neutron, proton-proton and neutron-neutron
scattering observables without the introduction of extra new parameters and
providing good phenomenological success.Comment: 15 pages, 6 figure
Deconstructing 1S0 nucleon-nucleon scattering
A distorted-wave method is used to analyse nucleon-nucleon scattering in the
1S0 channel. Effects of one-pion exchange are removed from the empirical phase
shift to all orders by using a modified effective-range expansion. Two-pion
exchange is then subtracted in the distorted-wave Born approximation, with
matrix elements taken between scattering waves for the one-pion exchange
potential. The residual short-range interaction shows a very rapid energy
dependence for kinetic energies above about 100 MeV, suggesting that the
breakdown scale of the corresponding effective theory is only 270MeV. This may
signal the need to include the Delta resonance as an explicit degree of freedom
in order to describe scattering at these energies. An alternative strategy of
keeping the cutoff finite to reduce large, but finite, contributions from the
long-range forces is also discussed.Comment: 10 pages, 2 figures (introduction revised, references added; version
to appear in EPJA
Causality bounds for neutron-proton scattering
We consider the constraints of causality and unitarity for the low-energy
interactions of protons and neutrons. We derive a general theorem that
non-vanishing partial-wave mixing cannot be reproduced with zero-range
interactions without violating causality or unitarity. We define and calculate
interaction length scales which we call the causal range and the Cauchy-Schwarz
range for all spin channels up to J = 3. For some channels we find that these
length scales are as large as 5 fm. We investigate the origin of these large
lengths and discuss their significance for the choice of momentum cutoff scales
in effective field theory and universality in many-body Fermi systems.Comment: 36 pages, 10 figures, 7 tables, version to appear in Eur. Phys. J.
Influence of conservation tillage and soil water content on crop yield in dryland compacted alfisol of Central Chile
Chilean dryland areas of the Mediterranean climate region are characterized by highly degraded and compacted soils, which require the use of conservation tillage systems to mitigate water erosion as well as to improve soil water storage. An oat (Avena sativa L. cv. Supernova-INIA) - wheat (Triticum aestivum L. cv. Pandora-INIA) crop rotation was established under the following conservation systems: no tillage (Nt), Nt + contour plowing (Nt+Cp), Nt + barrier hedge (Nt+Bh), and Nt + subsoiling (Nt+Sb), compared to conventional tillage (Ct) to evaluate their influence on soil water content (SWC) in the profile (10 to 110 cm depth), the soil compaction and their interaction with the crop yield. Experimental plots were established in 2007 and lasted 3 yr till 2009 in a compacted Alfisol. At the end of the growing seasons, SWC was reduced by 44 to 51% in conservation tillage systems and 60% in Ct. Soil water content had a significant (p < 0.05) interaction with tillage system and depth; Nt+Sb showed lower SWC between 10 to 30 cm, but higher and similar to the rest between 50 to 110 cm except for Ct. Although, SWC was higher in conservation tillage systems, the high values on soil compaction affected yield. No tillage + subsoiling reduced soil compaction and had a significant increment of grain yield (similar to Ct in seasons 2008 and 2009). These findings show us that the choice of conservation tillage in compacted soils of the Mediterranean region needs to improve soil structure to obtain higher yields and increment SWC
Cetrorelix suppresses the preovulatory LH surge and ovulation induced by ovulation-inducing factor (OIF) present in llama seminal plasma
<p>Abstract</p> <p>Background</p> <p>The purpose of the study was to determine if the effect of llama OIF on LH secretion is mediated by stimulation of the hypothalamus or pituitary gland.</p> <p>Methods</p> <p>Using a 2-by-2 factorial design to examine the effects of OIF vs GnRH with or without a GnRH antagonist, llamas with a growing ovarian follicle greater than or equal to 8 mm were assigned randomly to four groups (n = 7 per group) and <b>a) </b>pre-treated with 1.5 mg of GnRH antagonist (cetrorelix acetate) followed by 1 mg of purified llama OIF, <b>b) </b>pre-treated with 1.5 mg of cetrorelix followed by 50 micrograms of GnRH, <b>c) </b>pre-treated with a placebo (2 ml of saline) followed by 1 mg of purified llama OIF or <b>d) </b>pre-treated with a placebo (2 ml of saline) followed by 50 micrograms of GnRH. Pre-treatment with cetrorelix or saline was given as a single slow intravenous dose 2 hours before intramuscular administration of either GnRH or OIF. Blood samples for LH measurement were taken every 15 minutes from 1.5 hours before to 8 hours after treatment. The ovaries were examined by ultrasonography to detect ovulation and CL formation. Blood samples for progesterone measurement were taken every-other-day from Day 0 (day of treatment) to Day 16.</p> <p>Results</p> <p>Ovulation rate was not different (P = 0.89) between placebo+GnRH (86%) and placebo+OIF groups (100%); however, no ovulations were detected in llamas pre-treated with cetrorelix. Plasma LH concentrations surged (P < 0.01) after treatment in both placebo+OIF and placebo+GnRH groups, but not in the cetrorelix groups. Maximum plasma LH concentrations and CL diameter profiles did not differ between the placebo-treated groups, but plasma progesterone concentrations were higher (P < 0.05), on days 6, 8 and 12 after treatment, in the OIF- vs GnRH-treated group.</p> <p>Conclusion</p> <p>Cetrorelix (GnRH antagonist) inhibited the preovulatory LH surge induced by OIF in llamas suggesting that LH secretion is modulated by a direct or indirect effect of OIF on GnRH neurons in the hypothalamus.</p
First record and massive range extension of Hyalinobatrachium cappellei (Van Lidth de Jeude, 1904) (Anura, Centrolenidae) in Colombia
We report the first record of the Banded-limb Glassfrog, Hyalinobatrachium cappellei (Van Lidth de Jeude, 1904), in Colombia based on 2 specimens, 1 each from the municipalities of Cartagena del Chair&aacute; and Solano, department of Caquet&aacute;. The present record represents an additional amphibian species for the country, bringing the known total to 821 species and represents a massive range extension of 1,077 km southwest of the nearest known locality for H. cappellei in Venezuela.&nbsp
Nuclear forces from chiral EFT: The unfinished business
In spite of the great progress we have seen in recent years in the derivation
of nuclear forces from chiral effective field theory (EFT), some important
issues are still unresolved. In this contribution, we discuss the open problems
which have particular relevance for microscopic nuclear structure, namely, the
proper renormalization of chiral nuclear potentials and sub-leading many-body
forces.Comment: 16 pages, 3 figures; contribution to J. Phys. G, Special Issue, Focus
Section: Open Problems in Nuclear Structur
MicroRNAs in colorectal cancer
Colorectal cancer (CRC) is the third most common type of cancer worldwide, currently representing the most common gastrointestinal cancer with 13% of all malignant tumors. MicroRNAs (miRNAs) are small non-coding RNAs that repress the translation of target genes. Since their discovery, they have been shown to play an important role in the development of cancer, since they can act as tumor suppressors or oncogenes. A literature review was performed in different databases such as Medline, PubMed, Cochrane, nature, Wolters Kluwer, ScienceDirect, Scopus, SpringerLink, Wiley Online Library. Studies were included from 2003 to 2018. Colorectal cancer presents genetic heterogeneity, because it can develop in different ways, the pathway through which cancer occurs depends on the gene initially altered. The aberrant expression of microRNAs is implicated in the development of colorectal cancer and its progression. Three existing steps in the maturation of the microRNAs have been identified: 1) transcription of the pri-miRNA, 2) cleavage in the nucleus to form the pre-miRNA and 3) a final excision in the cytoplasm to form the mature microRNA. It has been discovered that miRNAs have an impact on cell proliferation, apoptosis, stress response, maintenance of stem cell potency and metabolism, all important factors in the etiology of cancer. The data analyzed in this article highlights the importance of the study of microRNAs in colorectal cancer, however, for the carcinogenic process, progression, therapeutic management and prognosis, more multicenter randomized clinical trials are needed with a detailed analysis
Towards a high precision calculation for the pion-nucleus scattering lengths
We calculate the leading isospin conserving few-nucleon contributions to pion
scattering on H, He, and He. We demonstrate that the strong
contributions to the pion-nucleus scattering lengths can be controlled
theoretically to an accuracy of a few percent for isoscalar nuclei and of 10%
for isovector nuclei. In particular, we find the -He scattering length
to be where the uncertainties are
due to ambiguities in the -N scattering lengths and few-nucleon effects,
respectively. To establish this accuracy we need to identify a suitable power
counting for pion-nucleus scattering. For this purpose we study the dependence
of the two-nucleon contributions to the scattering length on the binding energy
of H. Furthermore, we investigate the relative size of the leading two-,
three-, and four-nucleon contributions. For the numerical evaluation of the
pertinent integrals, aMonte Carlo method suitable for momentum space is
devised. Our results show that in general the power counting suggested by
Weinberg is capable to properly predict the relative importance of -nucleon
operators, however, it fails to capture the relative strength of - and
-nucleon operators, where we find a suppression by a factor of 5
compared to the predicted factor of 50. The relevance for the extraction of the
isoscalar -N scattering length from pionic H and He is discussed.
As a side result, we show that beyond the calculation of the -H
scattering length is already beyond the range of applicability of heavy pion
effective field theory.Comment: 24 pages, 14 figures, 10 table
Breast reconstruction: a review
Surgeons in the late 19th - 20th century performed radical mastectomies as the only possible treatment for breast cancers. Since then, the medical-surgical/scientific community has been constantly encouraged to develop and study different less invasive alternatives in breast reconstruction. Over time, locoregional perforator flap options have served as practical alternatives to implant-based reconstruction and abdominal flaps, especially in the setting of patients who have received radiation therapy or have a history of failed reconstruction, as they effectively fill the missing volume and respect the musculature of the donor site. Breast reconstruction using strategies with one of the different locoregional flaps can preserve the musculature and innervation of the post-mastectomy site, which manages to reduce possible adverse events. In addition to evaluating the anatomical characteristics of the defect and affected quadrant, it is essential to assess the patient's body constitution and the skills of the surgical team as well as microsurgery training when designing a reconstructive plan. Different research protocols should be developed in the study and development of new medical-surgical therapeutic alternatives; we suggest joint development with tissue engineering
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