Optimal control of a revenue management system with dynamic pricing facing linear demand

This paper considers a dynamic pricing problem over a finite horizon where demand for a product is a time‐varying linear function of price. It is assumed that at the start of the horizon there is a fixed amount of the product available. The decision problem is to determine the optimal price at each time period in order to maximize the total revenue generated from the sale of the product. In order to obtain structural results we formulate the decision problem as an optimal control problem and solve it using Pontryagin's principle. For those problems which are not easily solvable when formulated as an optimal control problem, we present a simple convergent algorithm based on Pontryagin's principle that involves solving a sequence of very small quadratic programming (QP) problems. We also consider the case where the initial inventory of the product is a decision variable. We then analyse the two‐product version of the problem where the linear demand functions are defined in the sense of Bertrand and we again solve the problem using Pontryagin's principle. A special case of the optimal control problem is solved by transforming it into a linear complementarity problem. For the two‐product problem we again present a simple algorithm that involves solving a sequence of small QP problems and also consider the case where the initial inventory levels are decision variables. Copyright © 2006 John Wiley & Sons, Ltd.     

Comparison of local and general anesthesia in tension-free (Lichtenstein) hernioplasty: a prospective randomized trial

To compare pulmonary effects, postoperative pain and fatigue, morbidity, patient satisfaction, and cost of different anesthetic techniques for inguinal hernia repair, 50 patients were randomized to local and general anesthesia groups (LA and GA). All patients received the same premedications and the same postoperative analgesic regimen. The standardized postoperative analgesic, intramuscular pyroxicam 20 mg, was given to all patients in the recovery room and an additional 20 mg on the same day was given as requested by each patient. Pulmonary function studies and arterial blood gas analysis were performed 1 h prior to the operation and at the postoperative 8th and 24th hours. All patients underwent Lichtenstein's tension-free hernioplasty. Postoperative pain and fatigue were registered 8 h and 24 h after the operation. A questionnaire was filled out by the patients, and they were asked to give grades for the general comfort of the anesthesia and the surgical procedure (1=worst, 10=best). Postoperative pulmonary function tests were significantly poorer in the GA group both on 8th- and 24th-hour measurements (P<0.05). Patients who underwent LA had significantly lower PCO₂ and higher PO₂ at the postoperative 8th hour (P<0.05). Mean postoperative pain and fatigue scores revealed a significant difference in favor of local anesthesia at only the 8th hour (P<0.05). There were two complications, one in each group (a hematoma in LA and a urinary retention in GA). Patient satisfaction grades were not different in the two groups. We conclude that LA in inguinal hernia repair does not adversely affect pulmonary functions, patients feel less pain, and patient satisfaction is comparable to that with GA. Electronic Publication     

Spinal metastasis of occult lung carcinoma causing cauda equina syndrome.

Cauda equina syndrome (CES) may be caused by tumor, herniated disc, trauma and spinal infections. However, CES due to occult lung cancer has not been reported in the literature. A 50-year-old man presented with a subacute CES caused by an intradural metastasis of an adenocarcinoma of the lung to the lumbosacral cauda fibers. His lumbosacral magnetic resonance imaging (MRI), showed a well-demarcated, intradural extramedullary mass lesion resembling a neurinoma at the L4/5 level. The patient underwent an L4-L5 laminectomy. The operative findings were also suggestive of neurinoma with involvement of three nerve roots, and a well-demarcated tumor without infiltration into the subarachnoid space. Although the findings of the operation were suggestive of neurinoma, final pathological diagnosis revealed metastatic carcinoma. Immunohistochemistry revealed clear cell adenocarcinoma metastasis. Chest X-ray and high resolution contrasted pulmonary computed tomography were normal. Positron emission tomography (PET) showed a lung mass, at the left apex. The patient was treated with chemotherapy and post-operative spinal radiotherapy was also performed. The CES resolved after the operation and the patient was followed up for 2 years with no recurrence. MRI of intradural cauda equina metastasis may be similar to that of intradural nerve sheath tumor. Surgery and postoperative radiotherapy may be effective for the treatment of CES due to lung carcinoma. Definitive diagnosis is by histopathological examination with immunohistochemistry. If the primary cancer cannot be detected by conventional radiological techniques, PET may be helpful.     

Clinical and epidemiologic evaluation of pressure ulcers in patients at a university hospital in Turkey.

OBJECTIVE: We sought to measure the incidence of pressure ulcer development at a university health center in Turkey, and to determine whether the Waterlow Pressure Sore Risk (PSR) Scale score predicted pressure ulcer development, stage, or number of ulcers. DESIGN: We prospectively evaluated patients who were hospitalized at our university-based medical center. SETTING AND SUBJECTS: We analyzed data from 22,834 patients hospitalized at the Baskent University Adana Teaching and Medical Research Center in Ankara, Turkey from January 1, 2004 to December 31, 2004, including 360 patients who developed pressure ulcers. INSTRUMENTS: The Waterlow PSR Scale was used to assess pressure ulcer risk. In addition, age, sex, the ward or unit in which the patient was hospitalized, reason for hospitalization, and location and stage of ulcers were collected on a data form designed specifically for this study. METHODS: A single nurse physiotherapist assessed all patients daily during their hospitalization. When a pressure ulcer was diagnosed by the nurse physiotherapist, a physician staged the pressure ulcers based on the US National Pressure Ulcer Advisory Panel (NPUAP) staging system. RESULTS: Three hundred sixty out of 22,834 patients developed 1 or more pressure ulcers, resulting in an incidence rate of 1.6%. Most ulcers (59.2%) occurred in patients hospitalized in the intensive care unit (n = 213). A positive correlation between the Waterlow PSR Scale score and number of ulcers per patient (r: 0.178, P < .01) was identified. No significant correlation was found linking Waterlow PSR Scale score and ulcer stage or the development of a single ulcer. CONCLUSION: We found significantly lower pressure ulcer incidence rates than those commonly reported in the literature, which we believe is principally attributable to short hospital stays and a strong emphasis on preventive nursing care. While high Waterlow PSR scale Scores correlated positively with development of multiple ulcers, this did not predict ulcer stage or the presence of a single pressure ulcer.     

Formulation and in Vitro-in Vivo Evaluation of Sustained-Release Lithium Carbonate Tablets

The release of lithium carbonate incorporated into polymethylmethacrylate, poly vinyl chloride, hy-drogenated vegetable oil, and carbomer matrix tablets was studied in vitro. The formulation containing 10% carbomer showed a sustained-release profile comparable to that of a standard, commercially available, sustained-release preparation containing 400 mg lithium carbonate embedded in a composite material. In vivo the newly formulated and standard sustained-release lithium carbonate tablets were compared to an oral solution and conventional lithium carbonate tablets in 12 healthy subjects. These crossover studies showed that the sustained-release tablets produced a flatter serum concentration curve than the oral solution and conventional tablet, without loss of total bioavailability.     

Synovial chondromatosis of four compartments of the knee: medial and lateral tibiofemoral spaces,patellofemoral joint and proximal tibiofibular joint

A case of synovial chondromatosis of the proximal tibiofibular joint in addition to lateral and medial tibiofemoral spaces and patellofemoral joint has been presented.     

Effects of granulocyte colony-stimulating factor on bacterial translocation due to burn wound sepsis

The presence of certain defects in both cellular and humoral immunity after thermal injury has been established. Likewise, the translocation of enteric bacteria to the mesenteric lymph nodes and to distant organs has also been observed following serious thermal injury. The effects of granulocyte colony-stimulating factor (G-CSF) on bacterial translocation, the small bowel mucosa, and cecal bacterial content were investigated in a rat model of burn wound sepsis in which albino Wistar rats were scalded over 30% of their bodies, after which the lesions were infected by 1×10⁸ colony-forming units (cfu)Pseudomonas aeruginosa. The control group was treated with 5% dextrose solution subcutaneously starting 2 days preburn, while the treatment group received 100μg/kg human G-CSF subcutaneously. On the 4th day post burn all animals were killed to examine the bowel and culture of the mesenteric lymph nodes (MLN), livers, and spleens. No significant differences were observed between the groups regarding the cecal bacterial content and small bowel; however, a difference was seen in the ratio of translocation in the MLN liver and spleen and quantitative MLN cultures. Based on these findings, G-CSF was thus found to be significantly effective in reducing bacterial translocation due to burn wound sepsis.     

Evaluation of prosthetic mesh closure in semiopen-abdomen patients

Abstract Background. To avoid the adverse consequences of abdominal compartment syndrome and to reduce the high mortality the celiotomy wound in patients with abdominal sepsis was closed without tension using prosthetic mesh. This produces a semiopen situation that permits staged reinterventions together with the functional reconstitution of the continuity of the abdominal wall. Material and Methods. Twenty-five patients with intra-abdominal sepsis of various causes were evaluated retrospectively to assess the results of semiopen management of the septic abdomen and reoperations on demand in severe peritonitis. All of the patients were in a state of neglected peritonitis, and had at least one failing organ system. The Mannheim Peritonitis Index (MPI) scoring system was used for stratification of abdominal sepsis. Results. The mean MPI score of 25 patients was 24, ranging 10 to 33. Eight (32%) patients were reexplored (MPI=21). There were overall 9 (36%) complications in patients with mean MPI score of 23. Six (24%) mesh-related complications (infection and enterocutaneous fistulas) developed (MPI=19). The mean MPI score of patients without complications was 24. Four (16%) patients died with index MPI score of 26 due to fulminant hepatitis, myocardial infarction, and multiple organ failure. The admission period averaged 63 days. Conclusions. In 25 critically ill patients with abdominal sepsis the mortality was lower than expected, relative to heterogeneous data from the literature; also, major complications occurred less frequently although the mean MPI score was high. The authors conclude that this approach is a reliable contribution to the complex treatment of these patients. Electronic Publication