1,317 research outputs found
Design and Experimental Analysis of Ventilated Walls and "Ice House" Roofs Applications in Warm Climates
This paper contains the findings of experimental research conducted to determine the effectiveness of ventilated walls and "ice house" roof applications in hot-humid climates. Ventilated wall and "ice house" roof is the type of construction which consists of interposing an additional wall or roof skin between the standard building envelope and the exterior environment. The new skin is separated from the building envelope by an air space, which is usually vented to the ambient environment. The primary objective of such construction is to eliminate or drastically reduce the effects of solar loading on the building envelope. The information presented in this paper can enable the designer to have a better understanding of how buildings might function at various times of the day and the season. Recommendations on applications of new buildings and retrofit of existing structures are presented here as well
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Isomeric triazines exhibit unique profiles of bioorthogonal reactivity.
Expanding the scope of bioorthogonal reactivity requires access to new and mutually compatible reagents. We report here that 1,2,4-triazines can be tuned to exhibit unique reaction profiles with biocompatible strained alkenes and alkynes. Computational analyses were used to identify candidate orthogonal reactions, and the predictions were experimentally verified. Notably, 5-substituted triazines, unlike their 6-substituted counterparts, undergo rapid [4 + 2] cycloadditions with a sterically encumbered strained alkyne. This unique, sterically controlled reactivity was exploited for dual bioorthogonal labeling. Mutually orthogonal triazines and cycloaddition chemistries will enable new multi-component imaging applications
Radiation-Induced Large Vessel Cerebral Vasculopathy in Pediatric Patients with Brain Tumors Treated with Proton Radiotherapy
Purpose
The purpose of this research is to evaluate the incidence, time to development, imaging patterns, risk factors, and clinical significance of large vessel cerebral vasculopathy in pediatric patients with brain tumors treated with proton radiotherapy.
Materials and Methods
A retrospective study was performed on 75 consecutive pediatric patients with primary brain tumors treated with proton radiotherapy. Radiation-induced large vessel cerebral vasculopathy (RLVCV) was defined as intracranial large vessel arterial stenosis or occlusion confirmed on MRA, CTA, and/or catheter angiography within an anatomic region with previous exposure to proton beam therapy and not present prior to radiotherapy. Clinical records were used to determine the incidence, timing, radiation dose to the large vessels, and clinical significance associated with the development of large vessel vasculopathy in these patients.
Results
RLVCV was present in 5/75 (6.7%) of patients and included tumor pathologies of craniopharyngioma (2), ATRT (1), medulloblastoma (1), and anaplastic astrocytoma (1). Median time from completion of radiotherapy to development was 1.5 years (mean 3.0 years; range 1.0-7.5 years). Neither mean age at time of radiotherapy (5.1 years) nor mean radiotherapy dose to the large vessels (54.5 Gy) were statistically significant risk factors. Four of the five patients with RLVCV presented with acute stroke, and demonstrated MRI evidence of acute infarcts in the expected vascular distributions. Angiography studies demonstrated collateral vessel formation in only two of the patients with RLVCV. No patients demonstrated acute hemorrhage or aneurysm. Two patients were treated with pial synangiomatosis surgery.
Conclusion
RLVCV can occur in pediatric patients with brain tumors treated with proton radiotherapy. Further studies are necessary to determine potential risk factors for large vessel vasculopathy with proton radiotherapy in comparison with conventional photon radiotherapy
Vortex Structures in YBa₂Cu₃O₇ (Invited)
Extensive small angle neutron scattering experiments have been conducted on the vortex system in YBa2Cu3O7 in a magnetic field range of 0.5 T≤H≤5 T, and with various orientations of the magnetic field with respect to the crystallographic axes. For H parallel to the c axis, the vortex lattice is oblique with two nearly equal lattice constants and an angle of 73°between primitive vectors. One principal axis of the vortex lattice coincides with the (110) direction of the crystal lattice. It is shown that this structure cannot be explained in the framework of a purely electrodynamic (London) model, and that it is intimately related to the in-plane anisotropy of the superconducting coherence length. When the field is inclined with respect to the c axis, the uniaxial anisotropy due to the layered crystal structure of YBa2Cu3O7 becomes relevant. The interplay between the square in-plane anisotropy and the uniaxial anisotropy leads to both a continous structural transition and a reorientation of the vortex lattice as a function of inclination angle. For the largest inclination angles, the vortex lattice decomposes into independent chains
Biochemical characterization of predicted Precambrian RuBisCO
The antiquity and global abundance of the enzyme, RuBisCO, attests to the crucial and longstanding role it has played in the biogeochemical cycles of Earth over billions of years. The counterproductive oxygenase activity of RuBisCO has persisted over billions of years of evolution, despite its competition with the carboxylase activity necessary for carbon fixation, yet hypotheses regarding the selective pressures governing RuBisCO evolution have been limited to speculation. Here we report the resurrection and biochemical characterization of ancestral RuBisCOs, dating back to over one billion years ago (Gyr ago). Our findings provide an ancient point of reference revealing divergent evolutionary paths taken by eukaryotic homologues towards improved specificity for CO2, versus the evolutionary emphasis on increased rates of carboxylation observed in bacterial homologues. Consistent with these distinctions, in vivo analysis reveals the propensity of ancestral RuBisCO to be encapsulated into modern-day carboxysomes, bacterial organelles central to the cyanobacterial CO2 concentrating mechanism
Vortex Lattice Symmetry and Electronic Structure in YBa₂Cu₃O₇
We report a small angle neutron scattering study of the vortex lattice in YBa2Cu3O7 in magnetic fields of 0.5≤H≤5 T applied along and close to the c axis. Over the entire field range, the vortices form an oblique lattice with two nearly equal lattice constants and an angle of 73°between primitive vectors. Numerical calculations suggest that variations of the superconducting order parameter near the vortex core are important in stabilizing this structure. An analysis that accounts for the fourfold symmetry of the vortex core qualitatively explains both the symmetry and the orientation of the observed vortex lattice. A quantitative explanation of our data will require calculations based on a realistic gap equation
Backlund Transformations, D-Branes, and Fluxes in Minimal Type 0 Strings
We study the Type 0A string theory in the (2,4k) superconformal minimal model
backgrounds, focusing on the fully non-perturbative string equations which
define the partition function of the model. The equations admit a parameter,
Gamma, which in the spacetime interpretation controls the number of background
D-branes, or R-R flux units, depending upon which weak coupling regime is
taken. We study the properties of the string equations (often focusing on the
(2,4) model in particular) and their physical solutions. The solutions are the
potential for an associated Schrodinger problem whose wavefunction is that of
an extended D-brane probe. We perform a numerical study of the spectrum of this
system for varying Gamma and establish that when Gamma is a positive integer
the equations' solutions have special properties consistent with the spacetime
interpretation. We also show that a natural solution-generating transformation
(that changes Gamma by an integer) is the Backlund transformation of the KdV
hierarchy specialized to (scale invariant) solitons at zero velocity. Our
results suggest that the localized D-branes of the minimal string theories are
directly related to the solitons of the KdV hierarchy. Further, we observe an
interesting transition when Gamma=-1.Comment: 17 pages, 3 figure
Trends in the medical management of patients with heart failure
BACKGROUND: Despite the availability of effective therapies, heart failure (HF) remains a highly prevalent disease and the leading cause of hospitalizations in the U.S. Few data are available, however, describing changing trends in the use of various cardiac medications to treat patients with HF and factors associated with treatment. The objectives of this population-based study were to examine decade-long trends (1995 - 2004) in the use of several cardiac medications in patients hospitalized with acute decompensated heart failure (ADHF) and factors associated with evidence-based treatment.
METHODS: We reviewed the medical records of 9,748 residents of the Worcester, MA, metropolitan area who were hospitalized with ADHF at all 11 central Massachusetts medical centers in 1995, 2000, 2002, and 2004.
RESULTS: Between 1995 and 2004, respectively, the prescription upon hospital discharge of beta-blockers (23%; 67%), angiotensin pathway inhibitors (47%; 55%), statins (5%; 43%), and aspirin (35%; 51%) increased markedly, while the use of digoxin (51%; 29%), nitrates (46%; 24%), and calcium channel blockers (33%; 22%) declined significantly; nearly all patients received diuretics. Patients in the earliest study year, those with a history of obstructive pulmonary disease or anemia, incident HF, non-specific symptoms, and women were less likely to receive beta blockers and angiotensin pathway inhibitors than respective comparison groups. In 2004, 82% of patients were discharged on at least one of these recommended agents; however, only 41% were discharged on medications from both recommended classes.
CONCLUSIONS: Our data suggest that opportunities exist to further improve the use of HF therapeutics
D-Branes and Fluxes in Supersymmetric Quantum Mechanics
Type 0A string theory in the (2,4k) superconformal minimal model backgrounds,
with background ZZ D-branes or R-R fluxes can be formulated non-perturbatively.
The branes and fluxes have a description as threshold bound states in an
associated one-dimensional quantum mechanics which has a supersymmetric
structure, familiar from studies of the generalized KdV system. The relevant
bound state wavefunctions in this problem have unusual asymptotics (they are
not normalizable in general, and break supersymmetry) which are consistent with
the underlying description in terms of open and closed string sectors. The
overall organization of the physics is very pleasing: The physics of the closed
strings in the background of branes or fluxes is captured by the generalized
KdV system and non-perturbative string equations obtained by reduction of that
system (the hierarchy of equations found by Dalley, Johnson, Morris and
Watterstam). Meanwhile, the bound states wavefunctions, which describe the
physics of the ZZ D-brane (or flux) background in interaction with probe FZZT
D-branes, are captured by the generalized mKdV system, and non-perturbative
string equations obtained by reduction of that system (the Painleve II hierachy
found by Periwal and Shevitz in this context).Comment: 41 pages, LaTe
Generating Entangled Two-Photon States with Coincident Frequencies
It is shown that parametric downconversion, with a short-duration pump pulse
and a long nonlinear crystal that is appropriately phase matched, can produce a
frequency-entangled biphoton state whose individual photons are coincident in
frequency. Quantum interference experiments which distinguish this state from
the familiar time-coincident biphoton state are described.Comment: Revised version (a typo was corrected) as published on PR
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