Hyperbolic Metamaterial Resonator-Antenna Scheme for Large, Broadband Emission Enhancement and Single Photon Collection

We model the broadband enhancement of single-photon emission from color centres in silicon carbide nanocrystals coupled to a planar hyperbolic metamaterial, HMM resonator. The design is based on positioning the single photon emitters within the HMM resonator, made of a dielectric index-matched with silicon-carbide material. The broadband response results from the successive resonance peaks of the lossy Fabry Perot structure modes arising within the high-index HMM cavity. To capture this broadband enhancement in the single photon emitters spontaneous emission, we placed a simple gold based cylindrical antenna on top of the HMM resonator. We analyzed the performance of this HMM coupled antenna structure in terms of the Purcell enhancement, quantum efficiency, collection efficiency and overall collected photon rate. For perpendicular dipole orientation relative to the interface, the HMM coupled antenna resonator leads to a significantly large spontaneous emission enhancement with Purcell factor of the order of 250 along with a very high average total collected photon rate, CPR of about 30 over a broad emission spectrum, 700 nm to 1000 nm. The peak CPR increases to about 80 at 900 nm, corresponding to the emission of silicon-carbide quantum emitters. This is a state of the art improvement considering the previous computational designs have reported a maximum average CPR of 25 across the nitrogen-vacancy centre emission spectrum, 600 nm to 800 nm with the highest value being about 40 at 650 nm

Pentagonal puckering in a sheet of amorphous graphene

Ordered graphene has been extensively studied. In this paper we undertake a first density functional study of it topologically disordered analogues of graphene, in the form of a random network, consisting predominantly of hexagonal rings, but also including pentagons and heptagons. After some preliminaries with crystalline material, we relax various random network models and find that the presence of carbon pentagons induce local curvature, thus breaking the initial planar symmetry, in some analogy with the case of fullerenes. Using density functional theory to calculate the total energy, we find that while the planar state is locally stable, there is a puckered state that has lower energy. The scale of the puckering is consistent with that expected with local maxima and minima associated with pentagons surrounded by larger rings; forming local "buckyball domes"

The Steady Spin Down Rate of 4U 1907+09

Using X-ray data from the Rossi X-Ray Timing Explorer (RXTE), we report the pulse timing results of the accretion powered high mass X-ray binary (HMXRB) pulsar 4U 1907+09 covering a time span of almost two years. We measured three new pulse periods in addition to the previously measured four pulse periods. We are able to connect pulse arrival times in phase for more than a year. The source has been spinning down almost at a constant rate with a spin down rate of \dot \nu = (-3.54 \pm 0.02) \times 10^{-14} Hz s ^{-1} for more than 15 years. Residuals of pulse arrival times yield a very low level of random walk noise strengths \sim 2 \times 10^{-20} rad ^{2} sec ^{-3} on a time scale of 383 days, which is four decades lower than that of the HMXRB pulsar Vela X-1. The noise strength is only a factor of 5 greater than that of the low mass X-ray binary pulsar (LMXRB) 4U 1626-67. The low level of the timing noise and the very stable spin down rate of 4U 1907+09 makes this source unique among the HMXRBs, providing another example, in addition to 4U 1626-67, of long term quiet spin down from an accreting source. These examples show that the extended quiet spin down episodes observed in the anomalous X-ray pulsars (AXPs) pulsars 1RXS J170849.0-400910 and 1E 2259+586 do not necessarly imply that these sources are not accreting pulsars.Comment: Submitted to MNRA

Sclerosing peritonitis presenting as complete mechanical bowel obstruction: A case report

Introduction: Sclerosing peritonitis or abdominal cocoon syndrome is characterized by small bowel loops completely encapsulated by a fibrocollagenous membrane in the center of the abdomen. Although cocooning of the abdomen is mostly seen in patients on peritoneal dialysis, it can occur de novo; it very rarely manifests as complete mechanical bowel obstruction.Case Presentation: A 46-year-old Asian man presented with complete mechanical bowel obstruction. He had previous attacks of partial bowel obstruction during the past 6 to 8 months, which was misdiagnosed as abdominal tuberculosis because tuberculosis is very prevalent in the region in which he lives. He took anti-tuberculosis therapy for 3 months but this did not result in resolution of his symptoms. This time he had diagnostic laparoscopy followed by laparotomy in which a fibrocollagenous membrane, resulting in entrapment of his bowel, was excised and his entire small bowel was freed. Postoperatively he again had a mild episode of partial bowel obstruction but this was relieved with a short course of steroids.Discussion: Sclerosing peritonitis is a rare benign etiology of complete mechanical bowel obstruction. Patients might have suffered recurrent attacks of partial bowel obstruction in the past that were falsely managed on lines of other conditions such as tuberculosis, especially in endemic areas like Pakistan or India.Conclusion: Sclerosing peritonitis is a rare benign diagnosis which can manifest as complete bowel obstruction and a high index of suspicion is required to diagnose it. Contrast-enhanced computed tomography of the abdomen is a useful radiological tool to aid in preoperative diagnosis. Diagnostic laparoscopy is usually confirmatory. Peritoneal sac excision and adhesiolysis is the treatment and a short course of steroids in relapsing symptoms

Disclosing bad news of cancer diagnosis: Patients\u27 preference for communication

The majority of relatives of cancer patients in Pakistan request their clinicians to adopt a do not tell approach while counselling the patients regarding their disease. The current study aimed to assess patients\u27 understanding of their disease and how they would prefer the physicians to deliver news about cancer diagnosis and its management plan. This was a cross-sectional study in which both patients and their immediate relatives were interviewed. The study enrolled 55 patients with six different types of cancers. The study showed that 35 (65.5%) patients did not know the stage of their illness at the time of diagnosis, while 40 (72.7%) patients did not know the current stage of their disease. In 22 (40%) cases, the patient\u27s family knew the diagnosis ahead of the patient, and 19 (86.3%) families asked the clinicians to hide the diagnosis from the patient. This study, which used a scoring questionnaire, demonstrates that specialist oncologists for breaking the bad news, family counselling, helping patients to figure out how to inform others, giving the news directly to the patient and the effects of cancer on daily life are preferred areas to communicate with cancer patients

Distribution of surface sediments off Indus delta on the continental shelf of Pakistan

Surface sediments from the continental shelf area off Indus delta were analysed for their textural characteristics and carbonate content. The sediments are largely silt, silty clay and clayey silty sand. Sandy fraction is dominant in the outer region with relatively high carbonate content. The study shows that distribution of carbonate in sediments off Indus delta continental shelf is controlled by the dilution of terrigenous material and its distance from source area

Syntheses and Step-by-Step Morphological Analysis of Nano-Copper-Decorated Carbon Long Fibers for Aerospace Structural Applications

Carbon long fiber/copper composites were prepared using electroless and electroplating methods with copper metal for potential aerospace applications. Carbon fibers were heat-treated at 450 °C followed by acid treatment before the metallization processes. Three different methods of metallization processes were applied: electroless silver deposition, electroless copper deposition and electroplating copper deposition. The metallized carbon fibers were subjected to copper deposition via two different routes. The first method was the electroless deposition technique in an alkaline tartrate bath using formaldehyde as a reducing agent of the copper ions from the copper sulphate solution. The second method was conducted by copper electroplating on the chemically treated carbon fibers. The produced carbon fiber/copper composites were extensively investigated by Field-Emission Scanning Electron Microscopy (FE-SEM) supported with an Energy Dispersive X-Ray Analysis (EDAX) unit to analyze the size, surface morphology, and chemical composition of the produced carbon long fiber/copper composites. The results show that the carbon fiber/copper composites prepared using the electroplating method had a coated type surface morphology with good adhesion between the copper coated layer and the surface of the carbon fibers. However, the carbon fiber/copper composites prepared using the electroless deposition had a decorated type morphology. Moreover, it was observed that the metallized carbon fibers using the silver method enhanced the electroless copper coating process with respect to the electroless copper coating process without silver metallization. The electrical conductivity of the carbon fiber/copper composites was improved by metallization of the carbon fibers using silver, as well as by the electrodeposition method