Orientational order on curved surfaces - the high temperature region

We study orientational order, subject to thermal fluctuations, on a fixed curved surface. We derive, in particular, the average density of zeros of Gaussian distributed vector fields on a closed Riemannian manifold. Results are compared with the density of disclination charges obtained from a Coulomb gas model. Our model describes the disordered state of two dimensional objects with orientational degrees of freedom, such as vector ordering in Langmuir monolayers and lipid bilayers above the hexatic to fluid transition.Comment: final version, 13 Pages, 2 figures, uses iopart.cl

B(H) Constitutive Relations Near H_c1 in Disordered Superconductors

We provide a self-contained account of the B vs. H constitutive relation near H_c1 in Type II superconductors with various types of quenched random disorder. The traditional Abrikosov result B ~ [ln (H - H_c1)]^{-2}, valid in the absence of disorder and thermal fluctuations, changes significantly in the presence of disorder. Moreover, the constitutive relations will depend strongly on the type of disorder. In the presence of point disorder, B ~ (H - H_c1)^{3/2} in three-dimensional (thick) superconductors, as shown by Nattermann and Lipowsky. In two-dimensional (thin film) superconductors with point disorder, B ~ (H - H_c1). In the presence of parallel columnar disorder, we find that B ~ exp[-C / (H - H_c1)] in three dimensions, while B ~ exp[-K / (H - H_c1)^{1/2}] in two dimensions. In the presence of nearly isotropically splayed disorder, we find that B ~ (H - H_c1)^{3/2} in both two and three dimensions.Comment: 37 pages, 12 figures included in text; submitted to Physica

Vortex Pinning and the Non-Hermitian Mott Transition

The boson Hubbard model has been extensively studied as a model of the zero temperature superfluid/insulator transition in Helium-4 on periodic substrates. It can also serve as a model for vortex lines in superconductors with a magnetic field parallel to a periodic array of columnar pins, due to a formal analogy between the vortex lines and the statistical mechanics of quantum bosons. When the magnetic field has a component perpendicular to the pins, this analogy yields a non-Hermitian boson Hubbard model. At integer filling, we find that for small transverse fields, the insulating phase is preserved, and the transverse field is exponentially screened away from the boundaries of the superconductor. At larger transverse fields, a ``superfluid'' phase of tilted, entangled vortices appears. The universality class of the transition is found to be that of vortex lines entering the Meissner phase at H_{c1}, with the additional feature that the direction of the tilted vortices at the transition bears a non-trivial relationship to the direction of the applied magnetic field. The properties of the Mott Insulator and flux liquid phases with tilt are also discussed.Comment: 20 pages, 12 figures included in text; to appear in Physical Review

Patient and physician attitudes towards salvage stereotactic radiosurgery or radiotherapy for brain metastases

The experience of patients with brain metastases treated with stereotactic radiosurgery (SRS) may shape attitudes towards salvage therapy. Furthermore, physician attitudes towards salvage therapy may differ based on specialty and experience. Our objective is to compare physician attitudes and patient experiences with SRS.BackgroundThe experience of patients with brain metastases treated with stereotactic radiosurgery (SRS) may shape attitudes towards salvage therapy. Furthermore, physician attitudes towards salvage therapy may differ based on specialty and experience. Our objective is to compare physician attitudes and patient experiences with SRS.Eligible patients with brain metastases treated with one course of SRS or fractionated stereotactic radiotherapy (FSRT) without whole brain radiotherapy (WBRT) in the definitive or postoperative setting at a single institution were surveyed from 11/2021 to 11/2022 regarding their perspectives on salvage therapy. A separate 11-question multi-disciplinary physician survey was distributed to residents, fellows and attendings at seven additional academic institutions in the US. Chi-square test and Mann-Whitney U test were used to assess differences.MethodsEligible patients with brain metastases treated with one course of SRS or fractionated stereotactic radiotherapy (FSRT) without whole brain radiotherapy (WBRT) in the definitive or postoperative setting at a single institution were surveyed from 11/2021 to 11/2022 regarding their perspectives on salvage therapy. A separate 11-question multi-disciplinary physician survey was distributed to residents, fellows and attendings at seven additional academic institutions in the US. Chi-square test and Mann-Whitney U test were used to assess differences.A total of 30 patients and 88 physicians were surveyed. Most patients reported being satisfied or very satisfied with initial SRS/FSRT (90%). When given an option between WBRT or SRS for salvage treatment, all patients favored SRS. The physicians consisted of radiation oncologists (69.3%), neurosurgeons (19.3%), medical oncologists (8.0%), and neuro-oncologists (3.4%). Most physicians were confident or very confident in their ability to discuss the risks and benefits of SRS for brain metastases (78.9%), but this was significantly lower if the patient had received prior SRS (56.6%, P<.001). In these cases, there were significant differences in response by medical specialty and confidence level (P<0.05).ResultsA total of 30 patients and 88 physicians were surveyed. Most patients reported being satisfied or very satisfied with initial SRS/FSRT (90%). When given an option between WBRT or SRS for salvage treatment, all patients favored SRS. The physicians consisted of radiation oncologists (69.3%), neurosurgeons (19.3%), medical oncologists (8.0%), and neuro-oncologists (3.4%). Most physicians were confident or very confident in their ability to discuss the risks and benefits of SRS for brain metastases (78.9%), but this was significantly lower if the patient had received prior SRS (56.6%, P<.001). In these cases, there were significant differences in response by medical specialty and confidence level (P<0.05).Patients and physicians view tumor control followed by long-term toxicity as the most important factors for salvage therapy after initial SRS for brain metastases.ConclusionsPatients and physicians view tumor control followed by long-term toxicity as the most important factors for salvage therapy after initial SRS for brain metastases

Biochemical characterization of prephenate dehydrogenase from the hyperthermophilic bacterium Aquifex aeolicus

A monofunctional prephenate dehydrogenase (PD) from Aquifex aeolicus was expressed as a His-tagged protein in Escherichia coli and was purified by nickel affinity chromatography allowing the first biochemical and biophysical characterization of a thermostable PD. A. aeolicus PD is susceptible to proteolysis. In this report, the properties of the full-length PD are compared with one of these products, an N-terminally truncated protein variant (Δ19PD) also expressed recombinantly in E. coli. Both forms are dimeric and show maximum activity at 95°C or higher. Δ19PD is more sensitive to temperature effects yielding a half-life of 55 min at 95°C versus 2 h for PD, and values of kcat and Km for prephenate, which are twice those determined for PD at 80°C. Low concentrations of guanidine-HCl activate enzyme activity, but at higher concentrations activity is lost concomitant with a multi-state pathway of denaturation that proceeds through unfolding of the dimer, oligomerization, then unfolding of monomers. Measurements of steady-state fluorescence intensity and its quenching by acrylamide in the presence of Gdn-HCl suggest that, of the two tryptophan residues per monomer, one is buried in a hydrophobic pocket and does not become solvent exposed until the protein unfolds, while the less buried tryptophan is at the active site. Tyrosine is a feedback inhibitor of PD activity over a wide temperature range and enhances the cooperativity between subunits in the binding of prephenate. Properties of this thermostable PD are compared and contrasted with those of E. coli chorismate mutase-prephenate dehydrogenase and other mesophilic homologs