The Orbit and Occultations of KH 15D

The unusual flux variations of the pre-main-sequence binary star KH 15D have been attributed to occultations by a circumbinary disk. We test whether or not this theory is compatible with newly available data, including recent radial velocity measurements, CCD photometry over the past decade, and photographic photometry over the past 50 years. We find the model to be successful, after two refinements: a more realistic motion of the occulting feature, and a halo around each star that probably represents scattering by the disk. The occulting feature is exceptionally sharp-edged, raising the possibility that the dust in the disk has settled into a thin layer, and providing a tool for fine-scale mapping of the immediate environment of a T Tauri star. However, the window of opportunity is closing, as the currently visible star may be hidden at all orbital phases by as early as 2008.Comment: To appear in ApJ [16 pages, 13 figures

Impact of preoperative therapy on patterns of recurrence in pancreatic cancer

AbstractBackgroundA theoretical advantage of preoperative therapy in pancreatic adenocarcinoma is that it facilitates the early treatment of micrometastases and reduces postoperative systemic recurrence.MethodsMedical records of 309 consecutive patients undergoing resection of adenocarcinoma in the head of the pancreas were reviewed. Survival was calculated using the Kaplan–Meier method. Associations between preoperative therapy and patterns of recurrence were determined using chi-squared analysis.ResultsPreoperative therapy was administered to 108 patients and upfront surgery was performed in 201 patients. Preoperative therapy was associated with a significantly longer median disease-free survival of 14 months compared with 12 months in patients submitted to upfront surgery (P = 0.035). The rate of local disease as a component of first site of recurrence was significantly lower with preoperative therapy (11.3%) than with upfront surgery (22.9%) (P = 0.016). Preoperative therapy was associated with a lower rate of hepatic metastasis (21.7%) than upfront surgery (34.3%) (P = 0.026). Preoperative therapy did not affect rates of peritoneal or pulmonary metastasis.ConclusionsPreoperative therapy for pancreatic cancer was associated with longer disease-free survival and lower rates of local and hepatic recurrences. These data support the use of preoperative therapy to reduce systemic and local failures after resection

Temperature Dependence of Radiation Induced Conductivity in Insulators

We report on measurements of Radiation Induced Conductivity (RIC) of thin film Low Density Polyethylene (LDPE) samples. RIC occurs when incident ionizing radiation deposits energy in a material and excites electrons into conduction states. RIC is calculated as the difference in sample conductivity under an incident flux and “dark current” conductivity under no incident radiation. The primary focus of this study is the temperature dependence of the steady state RIC over a wide range of absorbed dose rates, from cryogenic temperatures to well above room temperature. The measured RIC values are compared to theoretical predictions of dose rate and temperature dependence based on photoconductivity models developed for localized trap states in disordered semiconductors. We also investigated the variation of RIC as a function of material, applied electric field, and incident beam energy parameters

Control of magnetic anisotropy by orbital hybridization in (La0.67Sr0.33MnO3)n/(SrTiO3)n superlattice

The asymmetry of chemical nature at the hetero-structural interface offers an unique opportunity to design desirable electronic structure by controlling charge transfer and orbital hybridization across the interface. However, the control of hetero-interface remains a daunting task. Here, we report the modulation of interfacial coupling of (La0.67Sr0.33MnO3)n/(SrTiO3)n superlattices by manipulating the periodic thickness with n unit cells of SrTiO3 and n unit cells La0.67Sr0.33MnO3. The easy axis of magnetic anisotropy rotates from in-plane (n = 10) to out-of-plane (n = 2) orientation at 150 K. Transmission electron microscopy reveals enlarged tetragonal ratio > 1 with breaking of volume conservation around the (La0.67Sr0.33MnO3)n/(SrTiO3)n interface, and electronic charge transfer from Mn to Ti 3d orbitals across the interface. Orbital hybridization accompanying the charge transfer results in preferred occupancy of 3d3z2-r2 orbital at the interface, which induces a stronger electronic hopping integral along the out-of-plane direction and corresponding out-of-plane magnetic easy axis for n = 2. We demonstrate that interfacial orbital hybridization in superlattices of strongly correlated oxides may be a promising approach to tailor electronic and magnetic properties in device applications

What Is a Thing?

‘Thing’ in the titular question should be construed as having the utmost generality. In the relevant sense, a thing just is an entity, an existent, a being. The present task is to say what a thing of any category is. This task is, I believe, the primary one of any comprehensive and systematic metaphysics. Indeed, an answer provides the means for resolving perennial disputes concerning the integrity of the structure in reality—whether some of the relations among things are necessary merely given those relata themselves—and the intricacy of this structure—whether some things are more or less fundamental than others. After considering some reasons for thinking the generality of the titular question makes it unanswerable, I propound the methodology, original inquiry, required to answer it. The key to this methodology is adopting a singular perspective; confronting the world as merely the impetus to inquiry, one can attain an account of what a thing must be. Radical ontology is a systematic metaphysics—broadly Aristotelian, essentialist and nonhierarchical—that develops the consequences of this account. With it, it is possible to move past stalemate in metaphysics by revealing the grounds of a principled choice between seemingly incommensurable worldviews

Salmonella enterica Pulsed-Field Gel Electrophoresis Clusters, Minnesota, USA, 2001–2007

This procedure can help identify outbreaks of salmonellosis