Approximate Majority with Catalytic Inputs

Population protocols are a class of algorithms for modeling distributed computation in networks of finite-state agents communicating through pairwise interactions. Their suitability for analyzing numerous chemical processes has motivated the adaptation of the original population protocol framework to better model these chemical systems. In this paper, we further the study of two such adaptations in the context of solving approximate majority: persistent-state agents (or catalysts) and spontaneous state changes (or leaks). Based on models considered in recent protocols for populations with persistent-state agents, we assume a population with $n$ catalytic input agents and $m$ worker agents, and the goal of the worker agents is to compute some predicate over the states of the catalytic inputs. We call this model the Catalytic Input (CI) model. For $m = \Theta(n)$, we show that computing the parity of the input population with high probability requires at least $\Omega(n^2)$ total interactions, demonstrating a strong separation between the CI model and the standard population protocol model. On the other hand, we show that the simple third-state dynamics of Angluin et al. for approximate majority in the standard model can be naturally adapted to the CI model: we present such a constant-state protocol for the CI model that solves approximate majority in $O(n \log n)$ total steps with high probability when the input margin is $\Omega(\sqrt{n \log n})$. We then show the robustness of third-state dynamics protocols to the transient leaks events introduced by Alistarh et al. In both the original and CI models, these protocols successfully compute approximate majority with high probability in the presence of leaks occurring at each step with probability $\beta \leq O\left(\sqrt{n \log n}/n\right)$, exhibiting a resilience to leaks similar to that of Byzantine agents in previous works

Message Complexity of Population Protocols

The standard population protocol model assumes that when two agents interact, each observes the entire state of the other agent. We initiate the study of $\textit{message complexity}$ for population protocols, where the state of an agent is divided into an externally-visible $\textit{message}$ and an internal component, where only the message can be observed by the other agent in an interaction. We consider the case of $O(1)$ message complexity. When time is unrestricted, we obtain an exact characterization of the stably computable predicates based on the number of internal states $s(n)$: If $s(n) = o(n)$ then the protocol computes semilinear predicates (unlike the original model, which can compute non-semilinear predicates with $s(n) = O(\log n)$), and otherwise it computes a predicate decidable by a nondeterministic $O(n \log s(n))$-space-bounded Turing machine. We then introduce novel $O(\mathrm{polylog}(n))$ expected time protocols for junta/leader election and general purpose broadcast correct with high probability, and approximate and exact population size counting correct with probability 1. Finally, we show that the main constraint on the power of bounded-message-size protocols is the size of the internal states: with unbounded internal states, any computable function can be computed with probability 1 in the limit by a protocol that uses only $\textit{1-bit}$ messages

Diagnostic Accuracy of Age and Alarm Symptoms for Upper GI Malignancy in Patients with Dyspepsia in a GI Clinic: A 7-Year Cross-Sectional Study

<div><h3>Objectives</h3><p>We investigated whether using demographic characteristics and alarm symptoms can accurately predict cancer in patients with dyspepsia in Iran, where upper GI cancers and <em>H. pylori</em> infection are common.</p> <h3>Methods</h3><p>All consecutive patients referred to a tertiary gastroenterology clinic in Tehran, Iran, from 2002 to 2009 were invited to participate in this study. Each patient completed a standard questionnaire and underwent upper gastrointestinal endoscopy. Alarm symptoms included in the questionnaire were weight loss, dysphagia, GI bleeding, and persistent vomiting. We used logistic regression models to estimate the diagnostic value of each variable in combination with other ones, and to develop a risk-prediction model.</p> <h3>Results</h3><p>A total of 2,847 patients with dyspepsia participated in this study, of whom 87 (3.1%) had upper GI malignancy. Patients reporting at least one of the alarm symptoms constituted 66.7% of cancer patients compared to 38.9% in patients without cancer (p<0.001). Esophageal or gastric cancers in patients with dyspepsia was associated with older age, being male, and symptoms of weight loss and vomiting. Each single predictor had low sensitivity and specificity. Using a combination of age, alarm symptoms, and smoking, we built a risk-prediction model that distinguished between high-risk and low-risk individuals with an area under the ROC curve of 0.85 and acceptable calibration.</p> <h3>Conclusions</h3><p>None of the predictors demonstrated high diagnostic accuracy. While our risk-prediction model had reasonable accuracy, some cancer cases would have remained undiagnosed. Therefore, where available, low cost endoscopy may be preferable for dyspeptic older patient or those with history of weight loss.</p> </div

Vessel and voyage determinants of tanker freight rates and contract times

The behavior of shipping freight (charter) rates and the timing of shipping contracts affect the transportation costs of charterers and the operating cash flows of shipowners. Although the literature has established macroeconomic determinants of shipping freight rates, there has been no systematic investigation of microeconomic determinants of freight rates and the delivery time of chartered ships (the laycan period) in the tanker market. Therefore, the aim of this paper is to investigate the importance of vessel and contract specific factors in the determination of tanker freight rates and laycan periods in shipping contracts. Individual tanker shipping contracts from January 2006 to March 2009 are used to estimate freight rates and laycan periods using a system of simultaneous equations. The estimation results suggest that the duration of the laycan period is an important determinant of the shipping freight rate and vice versa. Other determinants of freight rates include the vessel's hull type, fixture deadweight utilization ratio, vessel age, and voyage routes. Determinants of the laycan period include the former determinants as well as the Baltic Dirty Tanker Index and its volatility.Freight rate Tanker Shipping routes Laycan

Has Management of Epidermoid Tumors of the Cerebellopontine Angle Improved? A Surgical Synopsis of the Past and Present

We compared the surgical outcomes of recent patients with cerebellopontine angle (CPA) epidermoids treated with advanced surgical tools with those of patients treated in earlier series. From November 2000 to June 2004, we treated 12 patients with epidermoid tumors. One patient had a strict CPA lesion. Tumors extended into the prepontine region in seven cases and supratentorially in two. In two cases the CPA was involved bilaterally. All patients but one underwent a lateral suboccipital approach in a semi-sitting position with microsurgical technique. Endoscopic assistance was used in cases with extensions beyond the CPA. In one case, a subtemporal route was used. The mean follow-up was 27 months (range, 8 to 50 months). There were no deaths. Total removal was achieved in 7 of the 10 patients with unilateral CPA epidermoids. Preoperative status improved in eight (80%) patients, particularly the function of cranial nerves (CNs) V and VII. Only two patients had permanent CN deficits. Complete excision with preservation of CN function should be the goals of management of epidermoids of the CPA. In some cases, these goals can be difficult to achieve, even with contemporary surgical equipment. Bilateral and extensive tumors should be removed in staged procedures. The function of CN V and CN VII may recover after decompression, but the outcome of symptoms related to CN VIII is less certain. The endoscope is a reliable tool for assessing the extension of epidermoids, but it cannot be used for tumor removal

Antibiotic therapy in inflammatory bowel disease: a systematic review and meta-analysis

The etiology of inflammatory bowel disease (IBD) is unknown but may relate to an unidentified bacterial pathogen or an immunological reaction to gut microbiota. Antibiotics have therefore been proposed as a therapy for Crohn's disease (CD) and ulcerative colitis (UC) to induce remission in active disease to prevent relapse. Current data are conflicting and we therefore conducted a systematic review of randomized controlled trials (RCTs) evaluating antibiotics in IBD. Only parallel group RCTs were considered eligible. Studies with adult patients receiving any dose of therapy for at least 7 days and up to 16 weeks for active disease, or at least 6 months of follow-up for preventing relapse in quiescent disease were analyzed. We included any antibiotics alone or in combination using predefined definitions of remission and relapse. Two reviewers independently assessed eligibility and extracted data. The primary outcome was remission or relapse using an intention-to-treat methodology. The data were summarized using relative risk (RR) and pooled using a random effects model. For active CD, there were 10 RCTs involving 1,160 patients. There was a statistically significant effect of antibiotics being superior to placebo (RR of active CD not in remission=0.85; 95% confidence interval (CI)=0.73–0.99, P=0.03). There was moderate heterogeneity between results (I²=48%) and a diverse number of antibiotics were tested (anti-tuberculosis therapy, macrolides, fluroquinolones, 5-nitroimidazoles, and rifaximin) either alone or in combination. Rifamycin derivatives either alone or in combination with other antibiotics appeared to have a significant effect at inducing remission in active CD. In perianal CD fistula there were three trials evaluating 123 patients using either ciprofloxacin or metronidazole. There was a statistically significant effect in reducing fistula drainage (RR=0.8; 95% CI=0.66–0.98) with no heterogeneity (I²=0%) and an number needed to treat 5 (95% CI=3–20). For quiescent CD, there were 3 RCTs involving 186 patients treated with different antibiotics combinations (all including antimycobacterials) vs. placebo. There was a statistically significant effect in favor of antibiotics vs. placebo (RR of relapse=0.62; 95% CI=0.46–0.84), with no heterogeneity (I²=0%). In active UC, there were 9 RCTs with 662 patients and there was a statistically significant benefit for antibiotics inducing remission (RR of UC not in remission=0.64; 95% CI=0.43–0.96). There was moderate heterogeneity (I²=69%) and antibiotics used were all different single or combination drugs. Antibiotic therapy may induce remission in active CD and UC, although the diverse number of antibiotics tested means the data are difficult to interpret. This systematic review is a mandate for further trials of antibiotic therapy in IBD

Do the urinary bladder and large bowel interact, in sickness or in health?: ICI-RS 2011

Normal functioning of the urinary bladder and the distal gut is an essential part of daily physiological activity coordinated by the peripheral and central nervous systems. Pathological changes in one of these organs may induce the development of cross-organ sensitization in the pelvis and underlie clinical co-morbidity of genitourinary and GI dysfunctions. Experimental human and animal data suggest that the bladder and distal colon interact under both normal and pathological conditions, however, the directions of these interactions can change dramatically depending on the nature and duration of the applied stimuli. This review article aimed to summarize the clinical data on colon-bladder cross-reflexes in healthy individuals, as well as in patients with co-morbid disorders. It also discusses currently used animal models, experimental approaches, and suggested mechanisms of colon-bladder cross-talk. Additionally, it provides an overview of the potential pharmacological targets to develop treatment options for patients with co-morbid disorders. Presented work resulted from the discussion of colon/bladder interactions during “Think Tank 9” presentations at the International Consultation on Incontinence Research Society meeting held in Bristol, UK, 2011