9,743 research outputs found
Consequences of Leading-Logarithm Summation for the Radiative Breakdown of Standard-Model Electroweak Symmetry
In the empirically sensible limit in which QCD, t-quark Yukawa, and
scalar-field-interaction coupling constants dominate all other Standard-Model
coupling constants, we sum all leading-logarithm terms within the perturbative
expansion for the effective potential that contribute to the extraction of the
Higgs boson mass via radiative electroweak symmetry breaking. A Higgs boson
mass of 216 GeV emerges from such terms, as well as a scalar-field-interaction
coupling constant substantially larger than that anticipated from conventional
spontaneous symmetry breaking. The sum of the effective potential's leading
logarithms is shown to exhibit a local minimum in the limit if the
QCD coupling constant is sufficiently strong, suggesting (in a multiphase
scenario) that electroweak physics may provide the mechanism for choosing the
asymptotically-free phase of QCD.Comment: latex using aip proceedings class. 8 page write-out of presentation
at MRST 2003 Conference (Syracuse
Higher Order Stability of a Radiatively Induced 220 GeV Higgs Mass
The effective potential for radiatively broken electroweak symmetry in the
single Higgs doublet Standard Model is explored to four sequentially subleading
logarithm-summation levels (5-loops) in the dominant Higgs self-interaction
couplant . We augment these results with all contributing leading
logarithms in the remaining large but sub-dominant Standard Model couplants
(t-quark, QCD and gauge couplants) as well as next to
leading logarithm contributions from the largest of these, the t-quark and QCD
couplants. Order-by-order stability is demonstrated for earlier leading
logarithm predictions of an order 220 GeV Higgs boson mass in conjunction with
fivefold enhancement of the value for over that anticipated from
conventional spontaneous symmetry breaking.Comment: revtex, 6 pages. Analysis and text is expanded in revised versio
The development and pilot of the university student embeddedness (USE) scale for student retention within universities: validation with an Australian student sample
A significant number of university students are leaving their institutions before completing their degrees. The present research project applied embeddedness theory, from organizational research, to understand student retention in a tertiary student population, and develop a quantitative instrument that measured university student embeddedness. In Study One, a mixed-methods approach was employed to determine whether the Fit (similarity between the student and the university), Links (count of relationships at university), and Sacrifice (losses upon leaving university) dimensions of embeddedness related to students’ self-reported reasons for remaining enrolled at their university. Qualitative results from 15 undergraduate students indicated that intent to remain could be understood within the embeddedness dimensions of Fit, Links, and Sacrifice. These themes were employed to build the University Student Embeddedness (USE) scale. The measure was examined against Rasch measurement model assumptions for each of its subscales using data collected from 299 Australian tertiary students. Study Two sought to examine exploratory evidence of the concurrent validity of the scores from this developed measure. Responses from a separate sample of 196 Australian tertiary students showed only the Fit scale significantly related to student intentions to stay at university. All USE scales correlated with academic-related skills and motivations. These results suggest that the Fit scale may be valuable in identifying students at risk of dropout. Early identification of “at risk” students may lead to the development of targeted retention interventions. However, the USE’s role in detection requires further validation and the development of consistent findings within other student cohorts
On the Standard Approach to Renormalization Group Improvement
Two approaches to renormalization-group improvement are examined: the
substitution of the solutions of running couplings, masses and fields into
perturbatively computed quantities is compared with the systematic sum of all
the leading log (LL), next-to-leading log (NLL) etc. contributions to
radiatively corrected processes, with n-loop expressions for the running
quantities being responsible for summing N^{n}LL contributions. A detailed
comparison of these procedures is made in the context of the effective
potential V in the 4-dimensional O(4) massless model,
showing the distinction between these procedures at two-loop order when
considering the NLL contributions to the effective potential V.Comment: 6 page
Malignancy within a tail gut cyst:a case of retrorectal carcinoid tumour
Purpose. Tailgut cysts with malignant transformation are rare entities. We discuss the diagnostic strategy and treatment of a malignancy within a tailgut cyst. Methods. In this study we report on the case of a 61-year-old man with a malignant neuroendocrine tumour arising within a tailgut cyst and an overview of the literature emphasising the histopathological characteristics and differential diagnosis. Results. Our patient presented with lower back pain, rectal pain, and increased urgency of defecation. MRI scan and CT-guided biopsy on histological analysis revealed a diagnosis of carcinoid tumour of the presacral space. The patient subsequently underwent an abdominoperineal excision of the rectum. Conclusions. This case highlights the importance of tailgut cysts as a differential diagnosis of presacral masses. It is a rare congenital lesion developing from remnants of the embryonic postanal gut and is predominantly benign in nature. Approximately half of cases remain asymptomatic; therefore, diagnosis is often delayed. Magnetic resonance imaging is the investigation of choice and an awareness of the possibility of malignant potential is critical to avoiding missed diagnosis and subsequent morbidity. Complete surgical excision allows accurate diagnosis, confirmation of oncological clearance, and prevention of mortality
High-Pressure Synthesis of a Pentazolate Salt
The pentazolates, the last all-nitrogen members of the azole series, have
been notoriously elusive for the last hundred years despite enormous efforts to
make these compounds in either gas or condensed phases. Here we report a
successful synthesis of a solid state compound consisting of isolated
pentazolate anions N5-, which is achieved by compressing and laser heating
cesium azide (CsN3) mixed with N2 cryogenic liquid in a diamond anvil cell. The
experiment was guided by theory, which predicted the transformation of the
mixture at high pressures to a new compound, cesium pentazolate salt (CsN5).
Electron transfer from Cs atoms to N5 rings enables both aromaticity in the
pentazolates as well as ionic bonding in the CsN5 crystal. This work provides a
critical insight into the role of extreme conditions in exploring unusual
bonding routes that ultimately lead to the formation of novel high nitrogen
content species
Radiative Electroweak Symmetry-Breaking Revisited
In the absence of a tree-level scalar-field mass, renormalization-group
methods permit the explicit summation of leading-logarithm contributions to all
orders of the perturbative series within the effective potential for
electroweak symmetry. This improvement of the effective
potential function is seen to reduce residual dependence on the renormalization
mass scale. The all-orders summation of leading logarithm terms involving the
dominant three couplings contributing to radiative corrections is suggestive of
a potential characterized by a plausible Higgs boson mass of 216 GeV. However,
the tree potential's local minimum at is restored if QCD is
sufficiently strong.Comment: revtex, 4 pages, 1 eps figure embedded in manuscript. Updated version
contains additional comments and corrects minor error
The impact of population-based faecal occult blood test screening on colorectal cancer mortality:a matched cohort study
BACKGROUND: Randomised trials show reduced colorectal cancer (CRC) mortality with faecal occult blood testing (FOBT). This outcome is now examined in a routine, population-based, screening programme. METHODS: Three biennial rounds of the UK CRC screening pilot were completed in Scotland (2000–2007) before the roll out of a national programme. All residents (50–69 years) in the three pilot Health Boards were invited for screening. They received a FOBT test by post to complete at home and return for analysis. Positive tests were followed up with colonoscopy. Controls, selected from non-pilot Health Boards, were matched by age, gender, and deprivation and assigned the invitation date of matched invitee. Follow-up was from invitation date to 31 December 2009 or date of death if earlier. RESULTS: There were 379 655 people in each group (median age 55.6 years, 51.6% male). Participation was 60.6%. There were 961 (0.25%) CRC deaths in invitees, 1056 (0.28%) in controls, rate ratio (RR) 0.90 (95% confidence interval (CI) 0.83–0.99) overall and 0.73 (95% CI 0.65–0.82) for participants. Non-participants had increased CRC mortality compared with controls, RR 1.21 (95% CI 1.06–1.38). CONCLUSION: There was a 10% relative reduction in CRC mortality in a routine screening programme, rising to 27% in participants
Ten per cent polarized optical emission from GRB 090102
The nature of the jets and the role of magnetic fields in gamma-ray bursts
(GRB) remains unclear. In a baryon-dominated jet only weak, tangled fields
generated in situ through shocks would be present. In an alternative model,
jets are threaded with large scale magnetic fields that originate at the
central engine and which accelerate and collimate the jets. The way to
distinguish between the models is to measure the degree of polarization in
early-time emission, however previous claims of gamma-ray polarization have
been controversial. Here we report that the early optical emission from GRB
090102 was polarized at the level of P=10+/-1%, indicating the presence of
large-scale fields originating in the expanding fireball. If the degree of
polarization and its position angle were variable on timescales shorter than
our 60-s exposure, then the peak polarization may have been larger than 10 per
cent.Comment: 16 pages, 4 figures. Published in Nature (2009), Vol. 462, p767-76
Buffalo National River Ecosystems - Part II
The priorities were established for the Buffalo National River Ecosystem Studies through meetings and correspondence with Mr. Roland Wauer and other personnel of the Office of Natural Sciences, Southwest Region of the National Park Service. These priorities were set forth in the appendix of contract no. CX 700050443 dated May 21, 1975
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