Closed Timelike Curves in Relativistic Computation

In this paper, we investigate the possibility of using closed timelike curves (CTCs) in relativistic hypercomputation. We introduce a wormhole based hypercomputation scenario which is free from the common worries, such as the blueshift problem. We also discuss the physical reasonability of our scenario, and why we cannot simply ignore the possibility of the existence of spacetimes containing CTCs.Comment: 17 pages, 5 figure

Phase transition in the collisionless regime for wave-particle interaction

Gibbs statistical mechanics is derived for the Hamiltonian system coupling self-consistently a wave to N particles. This identifies Landau damping with a regime where a second order phase transition occurs. For nonequilibrium initial data with warm particles, a critical initial wave intensity is found: above it, thermodynamics predicts a finite wave amplitude in the limit of infinite N; below it, the equilibrium amplitude vanishes. Simulations support these predictions providing new insight on the long-time nonlinear fate of the wave due to Landau damping in plasmas.Comment: 12 pages (RevTeX), 2 figures (PostScript

The Effects of Starburst Activity on Low Surface Brightness Disk Galaxies

Although numerous simulations have been done to understand the effects of intense bursts of star formation on high surface brightness galaxies, few attempts have been made to understand how localized starbursts would affect both the color and surface brightness of low surface brightness (LSB) galaxies. To remedy this, we have run 53 simulations involving bursts of star formation activity on LSB galaxies, varying both the underlying galaxy properties and the parameters describing the starbursts. We discovered that although changing the total color of a galaxy was fairly straightforward, it was virtually impossible to alter a galaxy's central surface brightness and thereby remove it from the LSB galaxy classification without placing a high (and fairly artificial) threshold for the underlying gas density. The primary effect of large amounts of induced star formation was to produce a centralized core (bulge) component which is generally not observed in LSB galaxies. The noisy morphological appearance of LSB galaxies as well as their noisy surface brightness profiles can be reproduced by considering small bursts of star formation that are localized within the disk. The trigger mechanism for such bursts is likely distant/weak tidal encounters. The stability of disk central surface brightness to these periods of star formation argues that the large space density of LSB galaxies at z = 0 should hold to substantially higher redshifts.Comment: 38 pages, 5 figures, 4 tables, tarred and compressed Also available on http://guernsey.uoregon.edu/~kare

Metformin Treatment Does Not Inhibit Growth of Pancreatic Cancer Patient-Derived Xenografts

There is currently tremendous interest in developing anti-cancer therapeutics targeting cell signaling pathways important for both cancer cell metabolism and growth. Several epidemiological studies have shown that diabetic patients taking metformin have a decreased incidence of pancreatic cancer. This has prompted efforts to evaluate metformin, a drug with negligible toxicity, as a therapeutic modality in pancreatic cancer. Preclinical studies in cell line xenografts and one study in patient-derived xenograft (PDX) models were promising, while recently published clinical trials showed no benefit to adding metformin to combination therapy regimens for locally advanced and metastatic pancreatic cancer. PDX models in which patient tumors are directly engrafted into immunocompromised mice have been shown to be excellent preclinical models for biomarker discovery and therapeutic development. We evaluated the response of four PDX tumor lines to metformin treatment and found that all four of our PDX lines were resistant to metformin. We found that the mechanisms of resistance may occur through lack of sustained activation of adenosine monophosphate-activated protein kinase (AMPK) or downstream reactivation of the mammalian target of rapamycin (mTOR). Moreover, combined treatment with metformin and mTOR inhibitors failed to improve responses in cell lines, which further indicates that metformin alone or in combination with mTOR inhibitors will be ineffective in patients, and that resistance to metformin may occur through multiple pathways. Further studies are required to better understand these mechanisms of resistance and inform potential combination therapies with metformin and existing or novel therapeutics

Subcutaneous Metastatic Adenocarcinoma: An Unusual Presentation of Colon Cancer – Case Report and Literature Review

Subcutaneous metastasis from a visceral malignancy is rare with an incidence of 5.3%. Skin involvement as the presenting sign of a silent internal malignancy is an even rarer event occurring in approximately 0.8%. We report a case of a patient who presented to her dermatologist complaining of rapidly developing subcutaneous nodules which subsequently proved to be metastatic colon cancer, and we provide a review of the literature

Causes and timing of 30-day rehospitalization from skilled nursing facilities after a hospital admission for pneumonia or sepsis

BACKGROUND: Pneumonia and sepsis are among the most common causes of hospitalization in the United States and often result in discharges to a skilled nursing facility (SNF) for rehabilitation. We described the timing and most common causes of 30-day unplanned hospital readmission following an index hospitalization for pneumonia or sepsis. METHODS AND FINDINGS: This national retrospective cohort study included adults ≥65 years who were hospitalized for pneumonia or sepsis and were discharged to a SNF between July 1, 2012 and July 4, 2015. We quantified the ten most common 30-day unplanned readmission diagnoses and estimated the daily risk of first unplanned rehospitalization for four causes of readmission (circulatory, infectious, respiratory, and genitourinary). The index hospitalization was pneumonia for 92,153 SNF stays and sepsis for 452,254 SNF stays. Of these SNF stays, 20.9% and 25.9%, respectively, resulted in a 30-day unplanned readmission. Overall, septicemia was the single most common readmission diagnosis for residents with an index hospitalization for pneumonia (16.7% of 30-day readmissions) and sepsis (22.4% of 30-day readmissions). The mean time to unplanned readmission was approximately 14 days overall. Respiratory causes displayed the highest daily risk of rehospitalization following index hospitalizations for pneumonia, while circulatory and infectious causes had the highest daily risk of rehospitalization following index hospitalizations for sepsis. The day of highest risk for readmission occurred within two weeks of the index hospitalization discharge, but the readmission risk persisted across the 30-day follow-up. CONCLUSION: Among older adults discharged to SNFs following a hospitalization for pneumonia or sepsis, hospital readmissions for infectious, circulatory, respiratory, and genitourinary causes occurred frequently throughout the 30-day post-discharge period. Our data suggests further study is needed, perhaps on the value of closer monitoring in SNFs post-hospital discharge and improved communication between hospitals and SNFs, to reduce the risk of potentially preventable hospital readmissions

Plasma wave echo experiment

Experimental observation of a new nonlinear plasma phenomenon, the plasma wave echo, is reported