Nucleation of PET crystallization by metal hydroxides

PET formulations containing small amounts of nonalkali metal hydroxides were prepared by extrusion from the melt. The efficiency of the hydroxides as nucleating agents was estimated from the elevation of T_cc, the crystallization temperature upon cooling from the melt, normalized for the purpose of comparison to a single convenient M_w (or the corresponding intrinsic viscosity). The results show that metal hydroxides capable of releasing water within the processing temperature interval of PET are effective nucleating agents for the crystallization of the polymer. Hydroxides releasing water out of said interval do not nucleate PET. There are two proposed nucleation mechanisms: (a) a localized severe hydrolysis of PET by the water released in the immediate neighborhood of the hydroxide particles and (b) a localized supercooling of the PET in the vicinity of the particles by the released water. The hydrolyzed PET of sharply reduced molecular weight has a T_cc significantly higher than the T_cc of the unhydrolyzed majority of the polymer. Upon cooling from the melt, and with the possible localized supercooling, the PET in the immediate vicinity of the hydroxide particles crystallizes first, nucleating the rest of the polymer. At present we can not verify whether both mechanisms operate concomitantly and which one of them is dominant.     

Definitive localization of isolated tracheoesophageal fistula using bronchoscopy and esophagoscopy for guide wire placement

PURPOSE: To aid in identification of isolated tracheoesophageal fistulas (TEF), many surgeons have recommended the bronchoscopic placement of a ureteric or Fogarty catheter. This method can fail because of intraoperative dislodgment of the catheter. The authors present a new technique that enables us to definitively isolate and treat all H-type fistulas. METHODS: Six cases of isolated TEF are presented consisting of 4 H-type fistulas, a proximal pouch fistula, and a recurrent TEF. Three of the patients had undergone a total of four prior failed operations at outside institutions using attempted bronchoscopic catheter placement. On all six patients, bronchoscopy was first performed where the fistula tract was noted in the trachea and a guide wire was passed through the fistula. After orotracheal intubation, the authors performed rigid esophagoscopy; the guide wire was identified and brought out through the mouth. This created a wire loop through the fistula. With the use of x-ray we were then able to visualize the level of the fistula and determine whether a cervical or thoracic approach should be used. Identification of the fistula intraoperatively was then facilitated by traction on the loop by the anesthesiologist. RESULTS: Five of the six TEFs were repaired with neck exploration; one required right thoracotomy. In all patients, the fistula was identified and divided. There were no recurrences or other complications. CONCLUSION: This new technique is a simple and definitive method in identification and treatment of isolated TEF.     

Risk factors for early infection of central venous catheters in pediatric patients

OBJECTIVE: To compare standard nurse-based pain therapy with a patient-controlled analgesia (PCA) regimen. DESIGN: Prospective, randomized study. SETTING: Single-institutional, clinical investigation in an urban, university-affiliated hospital. PARTICIPANTS: Sixty patients undergoing elective first-time cardiac surgery were included. INTERVENTIONS: In 30 patients, a standard analgesic regimen was used, and in 30 patients, a PCA regimen was used. The perioperative and postoperative management was similar for all patients. MEASUREMENTS AND MAIN RESULTS: Degree of sedation, satisfaction, and pain (by visual analog scale [VAS]) was assessed within the first 3 postoperative days. Vital capacity (VC) and forced expiratory volume in 1 second (FEV1) were measured using a portable spirometry system. Cortisol and troponin T (TnT) plasma levels were also measured. The expectation of pain was similar in both groups, and the postoperative pain score was significantly lower in the PCA than in the standard group throughout the study period. Significantly more piritramid was used in the PCA (total, 75.6 +/- 33.4 mg) than in the standard group (total, 20.1 +/- 31.9 mg). VC and FEV1 were significantly lower in the standard group compared with the PCA patients. Cortisol and TnT plasma levels were similar in both groups. Frequency of side effects were similar for both groups. CONCLUSION: Because of the beneficial effects with regard to degree of pain and satisfaction, pain management using PCA systems can be recommended for cardiac surgery patients. It appears to be superior to standard nurse-based pain therapy.     

On the crystallinity of poly(alkylbenzimidazole) salts

Poly(alkyldibenzimidazole) and poly(alkylbisbenzimidazole) having five, six, seven, and eight methylene groups in each repeat unit were synthesized. Salts of these polymers with strong acids, whose pK is 4.00 or less, were prepared. Weaker acids do not form salts with the poly(alkylbenzimidazole)s. It was found that polymers having an even number of methylene groups per repeat unit tend to form crystalline salts while those polymers having an odd number of methylene groups from only amorphous salts. From among the crystalline salts, those containing poly(bisbenzimidazole)s are more crystalline than their analogous poly(dibenzimidazole)s.     

Dispositional resistance to change: Measurement equivalence and the link to personal values across 17 nations.

The concept of dispositional resistance to change has been introduced in a series of exploratory and confirmatory analyses through which the validity of the Resistance to Change (RTC) Scale has been established (S. Oreg, 2003). However, the vast majority of participants with whom the scale was validated were from the United States. The purpose of the present work was to examine the meaningfulness of the construct and the validity of the scale across nations. Measurement equivalence analyses of data from 17 countries, representing 13 languages and 4 continents, confirmed the cross-national validity of the scale. Equivalent patterns of relationships between personal values and RTC across samples extend the nomological net of the construct and provide further evidence that dispositional resistance to change holds equivalent meanings across nations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sequential interactive evolution for finding high-quality topologies

Finding a diverse set of high-quality (HQ) topologies for a single-objective optimization problem using an evolutionary computation algorithm can be difficult without a reliable measure that adequately describes the dissimilarity between competing topologies. In this article, a new approach for enhancing diversity among HQ topologies for engineering design applications is proposed. The technique initially selects one HQ solution and then searches for alternative HQ solutions by performing an optimization of the original objective and its dissimilarity with respect to the previously found solution. The proposed multi-objective optimization approach interactively amalgamates user articulated preferences with an evolutionary search so as sequentially to produce a set of diverse HQ solutions to a single-objective problem. For enhancing diversity, a new measure is suggested and an approach to reducing its computational time is studied and implemented. To illustrate the technique, a series of studies involving different topologies represented as bitmaps is presented.