Pricing in Social Networks with Negative Externalities

We study the problems of pricing an indivisible product to consumers who are embedded in a given social network. The goal is to maximize the revenue of the seller. We assume impatient consumers who buy the product as soon as the seller posts a price not greater than their values of the product. The product's value for a consumer is determined by two factors: a fixed consumer-specified intrinsic value and a variable externality that is exerted from the consumer's neighbors in a linear way. We study the scenario of negative externalities, which captures many interesting situations, but is much less understood in comparison with its positive externality counterpart. We assume complete information about the network, consumers' intrinsic values, and the negative externalities. The maximum revenue is in general achieved by iterative pricing, which offers impatient consumers a sequence of prices over time. We prove that it is NP-hard to find an optimal iterative pricing, even for unweighted tree networks with uniform intrinsic values. Complementary to the hardness result, we design a 2-approximation algorithm for finding iterative pricing in general weighted networks with (possibly) nonuniform intrinsic values. We show that, as an approximation to optimal iterative pricing, single pricing can work rather well for many interesting cases, but theoretically it can behave arbitrarily bad

Elasto-Plastic Stress Analysis in Rotating Disks and Pressure Vessels Made of Functionally Graded Materials

Abstract A new elastio-plastic stress solution in axisymmetric problems (rotating disk, cylindrical and spherical vessel) is presented. The rotating disk (cylindrical and spherical vessel) was made of a ceramic/metal functionally graded material, i.e. a particle-reinforced composite. It was assumed that the material's plastic deformation follows an isotropic strain-hardening rule based on the von-Mises yield criterion. The mechanical properties of the graded material were modeled by the modified rule of mixtures. By assuming small strains, Hencky's stress-strain relation was used to obtain the governing differential equations for the plastic region. A numerical method for solving those differential equations was then proposed that enabled the prediction of stress state within the structure. Selected finite element results were also presented to establish supporting evidence for the validation of the proposed approach

Parameters of tissue iron overload and cardiac function in patients with thalassemia major and intermedia

Noninvasive T2∗ magnetic resonance imaging (MRI) assessment can stratify the risk of subsequent cardiac dysfunction in β-thalassemia major (TM) and β-thalassemia intermedia (TI) patients. The normal level of N-terminal pro B-type natriuretic peptides (NT-proBNP) can rule out acute heart failure. We aim to investigate the relation of NT-proBNP level, T2∗ MRI, and echocardiographic findings in TM and TI patients. In this cross-sectional study, 41 TM patients, 41 TI patients, and 41 healthy individuals (HI) were enrolled. NT-proBNP level, T2∗ MRI, and two-dimensional echocardiography were assessed for all patients and controls. There was statistically significant correlation between NT-proBNP levels and mitral inflow late diastolic velocity (r = -0.538; p = 0.006) in TM group. There was statistically significant correlation between NT-proBNP levels and tricuspid annulus systolic velocity (r = -0.438; p = 0.028), systolic velocity of septum (r = -0.472; p = 0.020), and mitral inflow early-to-late diastolic wave ratio (r = 0.592; p = 0.002) in TM group. Early diagnosis and treatment of myocardial iron overload are likely to prevent the mortality in patients with established ventricular dysfunction. Since NT-proBNP levels were not significantly increased in documented left ventricular (LV) diastolic dysfunction, this factor may not be sensitive for the detection of latent LV diastolic dysfunction in the early stages of disease progression

A family presenting with multiple endocrine neoplasia type 2B: A case report

<p>Abstract</p> <p>Introduction</p> <p>Multiple endocrine neoplasia 2B, a rare autosomal dominant syndrome, is characterized by early onset of medullary thyroid carcinoma, pheochromocytoma, marfanoid habitus and mucosal neuromas of the tongue, lips, inner cheeks and inner eyelids. Gangliomatosis of the gastrointestinal tract and its complications may also occur in patients with this disease.</p> <p>Case presentation</p> <p>We present the case of a 16-year-old Persian man diagnosed as having a non-invasive form of multiple endocrine neoplasia 2B (medullary thyroid cancer, mucosal neuroma of the tongue, lips and inner eyelids). Our patient, who had a positive family history of medullary thyroid cancer, was of normal height with no signs of marfanoid habitus.</p> <p>Conclusions</p> <p>Ophthalmological and oral manifestations of multiple endocrine neoplasia 2B, as in the case of our patient, are rare presentations of the disease; unfortunately in the case of our patient his condition had not been noted and acted upon until he presented to our department. The diagnosis in our patient's case was made only after his mother presented with the same condition. As a result, we emphasize that physicians should pay more attention to the oral and ocular signs of multiple endocrine neoplasia 2B in order to diagnose this fatal syndrome at an earlier phase.</p

Prevalence of Hiatal Hernia and Related Risk Factors to Laparoscopic Cholecystectomy Using the Hasson Technique

BACKGROUND AND OBJECTIVE: One of the complications of laparoscopic cholecystectomy is trocar incision hernia (TSIH: Trocar Site Incisional Hernia), which occurs almost exclusively in the navel area and could cause significant problems. The aim of this study was to evaluate the prevalence of hiatal hernia in laparoscopic cholecystectomy and identify the associated risk factors. METHODS: This cross sectional study was done on patients who underwent laparoscopic cholecystectomy during one year in different hospitals of Babol. Information including age, gender, BMI, diagnosis prior to surgery, duration of hospitalization, duration of surgery, the thickness of the lining of the gallbladder, surgical site infection and umbilical hernia during 12 months follow-up for patients were confirmed and examined. FINDINGS: Among 270 studied patients, there were 236 women (87.4%) and 34 men (12.59 %). Eleven patients (4.07%) during the 12-month follow-up; they had a hiatal hernia surgical site infection in the navel area (223.82-4.33: CI-95%, OR: 31.14) and BMI (60.18-1.72 CI-95%; OR: 10.21) were associated with increased incidence of inguinal hernias. There was no relationship between other variables and umbilical hernia. CONCLUSION: According to the results of this study obesity and surgical site infections have been linked with an increased incidence of inguinal hernias