748 research outputs found
Minimal Production of Prompt Gravitational Waves during Reheating
The inflationary reheating phase begins when accelerated expansion ends. As
all Standard Model particles are coupled to gravity, gravitational interactions
will lead to particle production. This includes the thermal bath, dark matter
and gravitational radiation. Here, we compute the spectrum of gravitational
waves from the inflatoncondensate during the initial phase of reheating. As
particular examples of inflation, we consider the Starobinsky model and
T-models, all of which are in good phenomenological agreement with CMB
anisotropy measurements. The T-models are distinguished by the shape of the
potential about its minimum and can be approximated by , where
is the inflaton. Interestingly, the shape of the gravitational wave
spectrum (when observed) can be used to distinguish among the models
considered. As we show, the Starobinsky model and T-models with , provide
very different spectra when compared to models with or . Observation
of multiple harmonics in the spectrum can be interpreted as a direct
measurement of the inflaton mass. Furthermore, the cutoff in frequency can be
used to determine the reheating temperature.Comment: 11 pages, 4 figure
An integrated multiple criteria preference ranking approach to the Canadian west coast port congestion conflict
An integrative conflict analysis approach, incorporating an Analytic Hierarchy Process (AHP) based preference ranking method into the Graph Model for Conflict Resolution (GMCR), is employed to investigate the Canadian west coast port congestion dispute. The Canadian west coast has historically been an important gateway connecting North America to Asia thanks to its specific geographical and strategic location. Despite successful operations and maintenance of the port facilities to handle international trade during the past few decades, the west coast is now facing increasing congestion problems, resulting in significant delays in transporting goods from the west coast to other parts of Canada and the USA. The strategic analyses carried out in this research suggest potential resolutions in which Canada would expand port facilities at various locations, encouraging traders to continue choosing the Canadian west coast as one of their trade gateways to North America
The Role of Vectors in Reheating
We explore various aspects concerning the role of vector bosons during the
reheating process. Generally, reheating occurs during the period of
oscillations of the inflaton condensate and the evolution of the radiation bath
depends on the inflaton equation of state. For oscillations about a quadratic
minimum, the equation of state parameter, , and the evolution of
the temperature, with respect to the scale factor is independent of the
spin of the inflaton decay products. However, for cases when , there is a
dependence on the spin, and here we consider the evolution when the inflaton
decays or scatters to vector bosons. We also investigate the gravitational
production of vector bosons as potential dark matter candidates. Gravitational
production predominantly occurs through the longitudinal mode. We compare these
results to the gravitational production of scalars.Comment: 37 pages, 9 Figure
Education in Time: Cohort Differences in Educational Attainment in African-American Twins
OBJECTIVES:Educational opportunities for African-Americans expanded throughout the 20(th) century. Twin pairs are an informative population in which to examine changes in educational attainment because each twin has the same parents and childhood socioeconomic status. We hypothesized that correlation in educational attainment of older twin pairs would be higher compared to younger twin pairs reflecting changes in educational access over time and potentially reflecting a "ceiling effect" associated with Jim Crow laws and discrimination. METHODOLOGY AND PRINCIPAL FINDINGS:We used data from 211 same-sex twin pairs (98 identical, 113 fraternal) in the Carolina African-American Twin Study of Aging who were identified through birth records. Participants completed an in-person interview. The twins were predominantly female (61%), with a mean age of 50 years (SD = 0.5). We found that older age groups had a stronger intra-twin correlation of attained educational level. Further analysis across strata revealed a trend across zygosity, with identical twins demonstrating more similar educational attainment levels than did their fraternal twin counterparts, suggesting a genetic influence. DISCUSSION:These findings suggest that as educational opportunities broadened in the 20th century, African-Americans gained access to educational opportunities that better matched their individual abilities
Searching for dark photon dark matter in LIGO O1 data
Dark matter exists in our Universe, but its nature remains mysterious. The remarkable sensitivity of the Laser Interferometer Gravitational-Wave Observatory (LIGO) may be able to solve this mystery. A good dark matter candidate is the ultralight dark photon. Because of its interaction with ordinary matter, it induces displacements on LIGO mirrors that can lead to an observable signal. In a study that bridges gravitational wave science and particle physics, we perform a direct dark matter search using data from LIGO’s first (O1) data run, as opposed to an indirect search for dark matter via its production of gravitational waves. We demonstrate an achieved sensitivity on squared coupling as ∼4×10−45, in a (1)B dark photon dark matter mass band around A∼4×10−13 eV. Substantially improved search sensitivity is expected during the coming years of continued data taking by LIGO and other gravitational wave detectors in a growing global network.Open access fees provided in whole or in part by the University of Oklahoma Libraries.Ye
Observation of second sound in graphite at temperatures above 100 K
Wavelike thermal transport in solids, referred to as second sound, has until
now been an exotic phenomenon limited to a handful of materials at low
temperatures. This has restricted interest in its occurrence and in its
potential applications. Through time-resolved optical measurements of thermal
transport on 5-20 {\mu}m length scales in graphite, we have made direct
observations of second sound at temperatures above 100 K. The results are in
qualitative agreement with ab initio calculations that predict wavelike phonon
hydrodynamics on ~ 1-{\mu}m length scale up to almost room temperature. The
results suggest an important role of second sound in microscale transient heat
transport in two-dimensional and layered materials in a wide temperature range
What is macroecology?
The symposium 'What is Macroecology?' was held in London on 20 June 2012. The event was the inaugural meeting of the Macroecology Special Interest Group of the British Ecological Society and was attended by nearly 100 scientists from 11 countries. The meeting reviewed the recent development of the macroecological agenda. The key themes that emerged were a shift towards more explicit modelling of ecological processes, a growing synthesis across systems and scales, and new opportunities to apply macroecological concepts in other research fields
Addition of T2-Guided Optical Tomography Improves Noncontrast Breast Magnetic Resonance Imaging Diagnosis.
BACKGROUND:
While dynamic contrast-enhanced magnetic resonance imaging (DCE MRI) is recognized as the most sensitive examination for breast cancer detection, it has a substantial false positive rate and gadolinium (Gd) contrast agents are not universally well tolerated. As a result, alternatives to diagnosing breast cancer based on endogenous contrast are of growing interest. In this study, endogenous near-infrared spectral tomography (NIRST) guided by T2 MRI was evaluated to explore whether the combined imaging modality, which does not require contrast injection or involve ionizing radiation, can achieve acceptable diagnostic performance. METHODS:
Twenty-four subjects-16 with pathologically confirmed malignancy and 8 with benign abnormalities-were simultaneously imaged with MRI and NIRST prior to definitive pathological diagnosis. MRIs were evaluated independently by three breast radiologists blinded to the pathological results. Optical image reconstructions were constrained by grayscale values in the T2 MRI. MRI and NIRST images were used, alone and in combination, to estimate the diagnostic performance of the data. Outcomes were compared to DCE results. RESULTS:
Sensitivity, specificity, accuracy, and area under the curve (AUC) of noncontrast MRI when combined with T2-guided NIRST were 94%, 100%, 96%, and 0.95, respectively, whereas these values were 94%, 63%, 88%, and 0.81 for DCE MRI alone, and 88%, 88%, 88%, and 0.94 when DCE-guided NIRST was added. CONCLUSION:
In this study, the overall accuracy of imaging diagnosis improved to 96% when T2-guided NIRST was added to noncontrast MRI alone, relative to 88% for DCE MRI, suggesting that similar or better diagnostic accuracy can be achieved without requiring a contrast agent
Sensitivity of MRI-Guided Near-Infrared Spectroscopy Clinical Breast Exam Data and Its Impact on Diagnostic Performance
In this study, data from breast MRI-guided near infrared spectroscopy (NIRS) exams delivered to 44 patients scheduled for surgical resection (ending in 16 benign and 28 malignant diagnoses) were analyzed using a spatial sensitivity metric to quantify the adequacy of the optical measurements for interrogating the tumor region of interest, as derived from the concurrent MRI scan. Along with positional sensitivity, the incorporation of spectral priors and the selection of an appropriate regularization parameter in the image reconstruction were considered, and found to influence the diagnostic accuracy of the recovered images. Once optimized, the MRI/NIRS data was able to differentiate the malignant from benign lesions through both total hemoglobin (p = 0.0037) and tissue optical index (p = 0.00019), but required the relative spatial sensitivity of the optical measurement data to each lesion to be above 1%. Spectral constraints implemented during the reconstruction were required to obtain statistically significant diagnostic information from images of H2O, lipids, and Tissue Optical Index (TOI). These results confirm the need for optical systems that have homogenous spatial coverage of the breast while still being able to accommodate the normal range of breast sizes
- …