Extracranial to intracranial vascular anastomosis for occlusive cerebrovascular disease: experience in 110 patients

In an attempt to ascertain the value of extra- to intracranial arterial bypass for cerebrovascular disease, the general topic of bypass surgery is reviewed and the results of this procedure in 110 patients are analyzed. The feasibility of high patency rates of the anastomosis with acceptably low permanent morbidity and operative mortality rates is demonstrated. Lesions producing transient ischemic attacks which previously were considered to be inoperable or inaccessible can be bypassed by this procedure, and there appears to be a dramatic improvement in the symptomotology of virtually all patients. Patients with a mild stroke or "progressive stroke" also appear to benefit from bypass, but the erratic natural history of these entities precludes irrefutable substantiation of this conclusion. Patients with moderate-to-serve neurological deficits do not appear to be improved by this procedure. In our group of 20 patients presenting with transient ischemic attacks who have had more than 3 years of follow-up, only one patient has suffered a stroke and that was located in the opposite hemisphere.     

Repeated Price Search

Consumers check few sites in online purchases. Previous research and experiments we perform demonstrate that consumers can not calculate the optimal strategy for price search. They use heuristics whose performance is better than random and less than optimal. To investigate online price search performance we survey student online textbook purchases. Students achieve good performance because they start with a good strategy and online market organization of marketplace and meta-search sites. An important factor is that algorithms at sites searched perform calculations that reduce the computational complexity of the search.     

Evaluation of Air Gap structures produced by wet etch of sacrificial dielectrics: Critical processes and reliability of Air Gap formation

Two Air Gap technologies were investigated concerning critical process steps. Both approaches use SiO₂ for sacrificial material and buffered HF wet etch chemistry. These critical processes include pre-wet-etch-concerns and wet-etch-concerns. The results of a special spacer etch-back process are shown. A buffer layer of SiO₂ was introduced to relax the requirements on the dry back-etch process. The oxidation of SiC and SiCN films during dry etching and resist stripping is an issue of both technologies, because this may lead to an undercut of the interconnect lines during the buffered HF treatment. Nevertheless, this can be successfully avoided by the application of appropriate oxygen (O₂) free process media. Furthermore, the shifting of mechanical behaviour of such structures as a result of wet-etch treatment is investigated. The intrinsic stress of cantilever SiC films has the capability to cause pull-off forces to interfaces which may result in film delamination.     

Diindenoperylene derivatives: A model to investigate the path from molecular structure via morphology to solar cell performance

Efficient organic electronic devices require a detailed understanding of the relation between molecular structure, thin film growth, and device performance, which is only partially understood at present. Here, we show that small changes in molecular structure of a donor absorber material lead to significant changes in the intermolecular arrangement within organic solar cells. For this purpose, phenyl rings and propyl side chains are fused to the diindenoperylene (DIP) molecule. Grazing incidence X-ray diffraction and variable angle spectroscopic ellipsometry turned out to be a powerful combination to gain detailed information about the thin film growth. Planar and bulk heterojunction solar cells with C60 as acceptor and the DIP derivatives as donor are fabricated to investigate the influence of film morphology on the device performance. Due to its planar structure, DIP is found to be highly crystalline in pristine and DIP:C60 blend films while its derivatives grow liquid-like crystalline. This indicates that the molecular arrangement is strongly disturbed by the steric hindrance induced by the phenyl rings. The high fill factor (FF) of more than 75% in planar heterojunction solar cells of the DIP derivatives indicates excellent charge transport in the pristine liquid-like crystalline absorber layers. However, bulk heterojunctions of these materials surprisingly result in a low FF of only 54% caused by a weak phase separation and thus poor charge carrier percolation paths due to the lower ordered thin film growth. In contrast, crystalline DIP:C60 heterojunctions lead to high FF of up to 65% as the crystalline growth induces better percolation for the charge carriers. However, the major drawback of this crystalline growth mode is the nearly upright standing orientation of the DIP molecules in both pristine and blend films. This arrangement results in low absorption and thus a photocurrent which is significantly lower than in the DIP derivative devices, where the liquid-like crystalline growth leads to a more horizontal molecular alignment. Our results underline the complexity of the molecular structure-device performance relation in organic semiconductor devices.     

Influence of silicon crystal defects and contamination on the electrical behavior of power devices

Since power devices require a thick electrically active n-type silicon layer with high resistivity and a large area, their electrical characteristics are extremely sensitive to contamination. If heavy metals diffuse into the silicon wafers during the high-temperature steps, an uncontrolled increase in the leakage current and the on-state voltage can be observed. Furthermore, current filamentation and instabilities of the electrical data can occur. It turned out that the optimization of the cleaning processes, high-temperature steps and gettering treatments alone is not sufficient to avoid such effects. It is also important to avoid silicon crystal defects by proper processing. A dramatic increase in the leakage current was correlated with the appearance of silicon defects decorated with heavy metals. As a consequence of the low doping level of the n-base, the blocking voltage and the failure rate due to cosmic radiation are sensitive to contaminating atoms acting as donors.     

Formalin treatment for intractable hemorrhagic cystitis: a review of the literature with 16 additional cases

Acute, exsanguinating hemorrhagic cystitis secondary to cyclophosphamide therapy, radiation therapy, or an infiltrating bladder tumor may be managed successfully with intravesical Formalin therapy. The indications for its use, the technique, success rates, and complications are discussed. This treatment was effective in 14 of 16 patients in the present series and 79 of 90 cases reported in the literature. Dilutions of 4% or less were as effective as a 10% dilution and were associated with far fewer complications. The early use of Formalin in the treatment of intractable hemorrhagic cystitis is recommended.     

Hartnup disease. Clinical, pathological, and biochemical observations

Hartnup disease is a rare genetic disorder of amino acid transport associated with variable and intermittent clinical abnormalities. A family is described in which three siblings had an intermittently progressive neurological disease and two of the affected siblings had the Hartnup-pattern aminoaciduria. Neuropathological examination of one case showed severe diffuse atrophy, generalized neuronal loss in the cortex, and Purkinje cell loss in the cerebellum. In vivo and in vitro studies of intestinal amino acid transport in the surviving sibling indicated a partial defect in the transport of several neutral amino acids (tryptophan, alanine, serine, and methionine) with normal transport of other neutral amino acids (threonine, phenylalanine, histidine, tyrosine, and isoleucine). Transport of glycine, proline, hydroxyproline, and the basic amino acids appeared normal.     

Effect of occupational and nonoccupational factors on the respiratory system of vinyl chloride and other workers

There are suggestions in the literature that vinyl chloride (VC) acts as a lung irritant. Respiratory questionnaires and lung function tests were administered to 174 chemical (VC) workers, 81 polyvinyl chloride (PVC) workers, 72 former VC workers, and 136 rubber workers, and 68 maintenance workers with exposure to VC, PVC, and rubber. Except for small airways obstruction associated with rubber, increased respiratory symptoms and decreased pulmonary function were not associated with working in chemicals, plastics, or rubber. Some increases in baseline pulmonary function were associated with VC exposure. Acute reductions in pulmonary function were observed in smokers working in chemicals, plastics, and rubber. Heavier cigarette smokers over 40 years of age had the most adversely affected respiratory system. Work was not associated with chronic respiratory effects, but all exposure groups experienced some acute respiratory insult.