Dual-gated bilayer graphene hot electron bolometer

Detection of infrared light is central to diverse applications in security, medicine, astronomy, materials science, and biology. Often different materials and detection mechanisms are employed to optimize performance in different spectral ranges. Graphene is a unique material with strong, nearly frequency-independent light-matter interaction from far infrared to ultraviolet, with potential for broadband photonics applications. Moreover, graphene's small electron-phonon coupling suggests that hot-electron effects may be exploited at relatively high temperatures for fast and highly sensitive detectors in which light energy heats only the small-specific-heat electronic system. Here we demonstrate such a hot-electron bolometer using bilayer graphene that is dual-gated to create a tunable bandgap and electron-temperature-dependent conductivity. The measured large electron-phonon heat resistance is in good agreement with theoretical estimates in magnitude and temperature dependence, and enables our graphene bolometer operating at a temperature of 5 K to have a low noise equivalent power (33 fW/Hz1/2). We employ a pump-probe technique to directly measure the intrinsic speed of our device, >1 GHz at 10 K.Comment: 5 figure

Timing Constraints of In Vivo Gag Mutations during Primary HIV-1 Subtype C Infection

Background: Aiming to answer the broad question “When does mutation occur?” this study examined the time of appearance, dominance, and completeness of in vivo Gag mutations in primary HIV-1 subtype C infection. Methods: A primary HIV-1C infection cohort comprised of 8 acutely and 34 recently infected subjects were followed frequently up to 500 days post-seroconversion (p/s). Gag mutations were analyzed by employing single-genome amplification and direct sequencing. Gag mutations were determined in relation to the estimated time of seroconversion. Time of appearance, dominance, and completeness was compared for different types of in vivo Gag mutations. Results: Reverse mutations to the wild type appeared at a median (IQR) of 62 (44;139) days p/s, while escape mutations from the wild type appeared at 234 (169;326) days p/s (p<0.001). Within the subset of mutations that became dominant, reverse and escape mutations appeared at 54 (30;78) days p/s and 104 (47;198) days p/s, respectively (p<0.001). Among the mutations that reached completeness, reverse and escape mutations appeared at 54 (30;78) days p/s and 90 (44;196) days p/s, respectively (p = 0.006). Time of dominance for reverse mutations to and escape mutations from the wild type was 58 (44;105) days p/s and 219 (90;326) days p/s, respectively (p<0.001). Time of completeness for reverse and escape mutations was 152 (100;176) days p/s and 243 (101;370) days p/s, respectively (p = 0.001). Fitting a Cox proportional hazards model with frailties confirmed a significantly earlier time of appearance (hazard ratio (HR): 2.6; 95% CI: 2.3–3.0), dominance (4.8 (3.4–6.8)), and completeness (3.6 (2.3–5.5)) of reverse mutations to the wild type Gag than escape mutations from the wild type. Some complex mutational pathways in Gag included sequential series of reversions and escapes. Conclusions: The study identified the timing of different types of in vivo Gag mutations in primary HIV-1 subtype C infection in relation to the estimated time of seroconversion. Overall, the in vivo reverse mutations to the wild type occurred significantly earlier than escape mutations from the wild type. This shorter time to incidence of reverse mutations remained in the subsets of in vivo Gag mutations that reached dominance or completeness

A Controversy That Has Been Tough to Swallow: Is the Treatment of Achalasia Now Digested?

Esophageal achalasia is a rare neurodegenerative disease of the esophagus and the lower esophageal sphincter that presents within a spectrum of disease severity related to progressive pathological changes, most commonly resulting in dysphagia. The pathophysiology of achalasia is still incompletely understood, but recent evidence suggests that degeneration of the postganglionic inhibitory nerves of the myenteric plexus could be due to an infectious or autoimmune mechanism, and nitric oxide is the neurotransmitter affected. Current treatment of achalasia is directed at palliation of symptoms. Therapies include pharmacological therapy, endoscopic injection of botulinum toxin, endoscopic dilation, and surgery. Until the late 1980s, endoscopic dilation was the first line of therapy. The advent of safe and effective minimally invasive surgical techniques in the early 1990s paved the way for the introduction of laparoscopic myotomy. This review will discuss the most up-to-date information regarding the pathophysiology, diagnosis, and treatment of achalasia, including a historical perspective. The laparoscopic Heller myotomy with partial fundoplication performed at an experienced center is currently the first line of therapy because it offers a low complication rate, the most durable symptom relief, and the lowest incidence of postoperative gastroesophageal reflux

Alterações da motilidade esofagiana em pacientes cirróticos com varizes de esôfago não submetidos a tratamento endoscópico Esophageal motor disorders in cirrhotic patients with esophageal varices non-submitted to endoscopic treatment

RACIONAL: A cirrose hepática apresenta como uma das principais causas de morbimortalidade, a hipertensão porta com o desenvolvimento de varizes esofagianas, possibilidade de hemorragia digestiva alta e agravamento da insuficiência hepática. É importante identificar fatores preditivos causais ou agravantes desta condição e se possível, preveni-los. Nos últimos anos tem se observado a associação de distúrbios motores de esôfago e de refluxo gastroesofágico em pacientes cirróticos com varizes de esôfago. OBJETIVOS: Estudar a prevalência dos distúrbios de motilidade esofagiana e, entre eles, da motilidade esofagiana ineficaz, neste grupo de pacientes e seus possíveis fatores preditivos. MÉTODOS: Avaliaram-se de maneira prospectiva, 74 pacientes com cirrose hepática e varizes esofagianas diagnosticadas por endoscopia digestiva alta, virgens de tratamento endoscópico terapêutico. Todos foram submetidos a um protocolo de investigação clínica, a esofagomanometria e 55 pacientes também realizaram pHmetria esofagiana ambulatorial. RESULTADOS: Alterações da motilidade esofagiana foram observadas em 44 pacientes (60%), sendo a mais prevalente a motilidade esofagiana ineficaz, verificada em 28%. Refluxo anormal foi encontrado em 35% dos pacientes. Não houve correlação entre anormalidade manométrica em geral e motilidade esofagiana ineficaz, em particular, e a presença de sintomas esofagianos ou típicos de doença do refluxo, refluxo anormal, a gravidade da doença, a presença de ascite e o calibre das varizes. CONCLUSÕES: A maioria dos cirróticos com varizes esofagianas não submetidos a tratamento endoscópico apresenta distúrbios motores do esôfago, sem fatores preditivos identificáveis. A importância clínica desses achados necessita de maior aprofundamento na questão, para elucidar seu papel definitivo.<br>BACKGROUND: The hepatic cirrhosis has as one of the main morbid-mortality causes, the portal hypertension with the development of esophageal varices, the possibility of a digestive hemorrhage and worsening of hepatic insufficiency. It is important to identify causal predictive or aggravating factors and if possible to prevent them. In the last years, it has been observed the association of esophageal motor disorders and gastro-esophageal reflux in cirrhotic patients with esophageal varices. AIMS: To study the prevalence of the esophageal motility disorders and among them, the ineffective esophageal motility, in patients with hepatic cirrhosis and esophageal varices, without previous endoscopic therapeutic and the predictives factors. METHODS: Prospectively, it has been evaluate 74 patients suffering from liver cirrhosis and esophagic varices, without previous endoscopic treatment. All of them were submitted to a clinical protocol, esophageal manometry and 55 patients also held the ambulatory esophageal pHmetry. RESULTS: Esophageal motility disorders have been found in 44 patients (60%). The most prevalent was the ineffective esophageal motility, observed in 28%. The abnormal reflux disease was diagnosed through the pHmetry in 35% of the patients. There were no correlation between the manometrical abnormality in general and the ineffective esophageal motility in particular and the esophageal or gastroesophageal reflux disease symptoms, the abnormal reflux, the disease seriousness, the ascites presence and the gauge of the varices. CONCLUSIONS: The majority of cirrhotic patients with non-treated esophageal varices present esophageal motor disorders. No predictive factor was found. The clinical relevance of these findings need more researches in the scope to define the real meaning of theses abnormalities