857 research outputs found

    Surface properties of solids using a semi-infinite approach and the tight-binding approximation

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    A semi-infinite approach (rather than a slab method or finite number of layers) is used to treat surface properties such as wave functions, energy levels, and Fermi surfaces of semi-infinite solids within the tight-binding (TB) approximation. Previous single-band results for the face-centered cubic lattice with a (111) surface and for the simple cubic lattice with a (001) surface are extended to semi-infinite layers, while the extension to calculations of other surfaces is straightforward. Treatment of more complicated systems is illustrated in the calculation of the graphite (0001) surface. Four interacting bands are considered in the determination of the wave functions, energies, and Fermi surface of the graphite (0001) surface. For the TB model used, the matrix elements in the secular determinants for the semi-infinite solid and for the infinite bulk solid obey the same expressions, and the wave functions are closely related. Accordingly, the results for the bulk system can then be directly applied to the semi-infinite one. The main purpose of the present paper is to provide wave functions and other properties used elsewhere to treat phenomena such as scanning tunneling microscopy and electron transfer rates at electrodes

    A theoretical model of scanning tunneling microscopy: Application to the graphite (0001) and Au(111) surfaces

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    An expression for the scanning tunneling microscopy (STM) current between the tip and sample is presented using first-order perturbation theory for a two-Hamiltonian formalism ("reactants" and "products"). The calculated STM current depends on the square of the sample-tip matrix elements, averaged over a selection of random points in wave vector space. In the limit of low voltage and temperature, this averaging is over the Fermi surface of the sample. The model is applied to the graphite (0001) and Au(111) surfaces using a simple model (chain) of a tungsten tip and the tight-binding approximation. Comparisons with experiments and with the result for graphite obtained by Tersoff and Lang using a molybdenum tip are given. The theory is applied elsewhere to STM of adsorbates

    Capture on High Curvature Region: Aggregation of Colloidal Particle Bound to Giant Phospholipid Vesicles

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    A very recent observation on the membrane mediated attraction and ordered aggregation of colloidal particles bound to giant phospholipid vesicles (I. Koltover, J. O. R\"{a}dler, C. R. Safinya, Phys. Rev. Lett. {\bf 82}, 1991(1999)) is investigated theoretically within the frame of Helfrich curvature elasticity theory of lipid bilayer fluid membrane. Since the concave or waist regions of the vesicle possess the highest local bending energy density, the aggregation of colloidal beads on these places can reduce the elastic energy in maximum. Our calculation shows that a bead in the concave region lowers its energy ∟20kBT\sim 20 k_B T. For an axisymmetrical dumbbell vesicle, the local curvature energy density along the waist is equally of maximum, the beads can thus be distributed freely with varying separation distance.Comment: 12 pages, 2 figures. REVte

    Efficacy of the intracorporeal one-hand tie technique for renal pedicle control during hand-assisted retroperitoneoscopic nephroureterectomy

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    AbstractObjectiveThis study examined the efficacy of the intracorporeal one-hand tie technique for renal pedicle control during hand-assisted retroperitoneoscopic nephroureterectomy (HARN).MethodsThe intracorporeal one-hand tie technique was conducted in 32 consecutive patients with upper tract urothelial cancer that underwent HARN and open bladder cuff excision.ResultsAll suture ligatures were successful in securing the renal vessels, except one minor venous bleeding that occurred during vessel transection, which was then controlled by additional clips. The process of controlling the renal pedicle took an average of 12.4 minutes (range, 8–30 minutes). No pedicle control related morbidities were noted. By sparing the usage of endovascular clips and staplers, operative costs were reduced and associated malfunctions eliminated.ConclusionThe intracorporeal one-hand tie technique is an easy, reliable, and cost-effective method in controlling the renal pedicle during HARN. Its efficacy in pedicle control is beyond doubt

    Acquisition of skills in digital rectal examination through supervised patient examination with real-time feedback in transrectal sonography room

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    AbstractObjectiveTo assess the acquisition digital rectal examination (DRE) skills by medical students through an alternative teaching method.Materials and methodsMedical students at the National Cheng-Kung University Hospital, Tainan, Taiwan in 2009 were assigned to receive training through supervised rectal examination (DRE) with real-time feedback in a transrectal sonography room during their standard urologic rotation. Students completed a questionnaire (before and after the training) regarding their experiences in performing DRE to assess their confidence levels. Direct observation of practical skills (DOPS) was used to assess the students' competence in performing DRE at the end of urologic rotation.ResultsA total of 75 students received the questionnaire, of which 72 (96%) responded. On average, every student had an experience of 6.6 supervised patient examinations with real-time feedback in a transrectal sonography room. Following the training, students were more confident in their ability to give an opinion based on their findings related to DRE. The overall rate of the students' ability to interpret the DRE findings after urologic rotation improved from 69% to 100% for identification of the prostate, from 14% to 60% for assessment of prostate size, from 32% to 95% to describe prostate consistency accurately, and from 9.8% to 64% to identify overt prostate cancer from benign prostate hyperplasia. All students met expectations or were above expectations according to the grading scale of performing DOPS.ConclusionStudents' skills and confidence with regard to performing DRE were improved significantly through supervised examination with real-time feedback in a transrectal sonography room

    A Model of Optimal Capital Sucture with Stochastic Interest Rates

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    This paper develops a model of optimal capital structure with stochastic interest rate which is assumed to follow a mean-reverting process. Closed-form solutions are obtained for both the value of the firm and the value of its risky debt. The paper finds that the current level and the long-run mean of the interest rate process play distinctive roles in our integrated model. The current level of the interest rate is critical in the pricing of risky bonds, while the long-run mean plays a key role in the determination of a firm’s optimal capital sucture such as the optimal coupon rate and leverage ratio. Our findings demonsate that a model of optimal capital sucture with a constant interest rate cannot price risky bonds and determine the optimal capital sucture simultaneously in a satisfactory manner. Furthermore, our numerical results indicate that the correlation between the stochastic interest rate and the asset return of a firm has little impact on the firm’s optimal capital structure

    Expression of glypican 3 in placental site trophoblastic tumor

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    <p>Abstract</p> <p>Background</p> <p>Glypican-3 (GPC3) is a membrane-bound heparan sulfate proteoglycan that functions in embryonic cell growth and differentiation and is highly expressed in the placenta. GPC3 is mutated in Simpson-Golabi-Behmel syndrome, which is characterized by tissue overgrowth and an increased risk of embryonal malignancies. GPC3 has also been implicated in sporadic cancer, particularly hepatocellular carcinoma, for which it has been shown to be a useful diagnostic marker. Although GPC3 expression has been studied in non-neoplastic placental tissue, its presence in gestational trophoblastic diseases has not been previously explored. The purpose of this study was to investigate the immunohistochemical expression of GPC3 in placental site trophoblastic tumor (PSTT), a very rare gestational trophoblastic neoplasm which may be morphologically confused with non-trophoblastic tumors, and to assess its possible utility as a diagnostic marker.</p> <p>Methods</p> <p>Fifteen cases of PSTT, as well as samples from placental site nodule (PSN) (n = 2), leiomyosarcoma (n = 1), leiomyoma (n = 1), invasive cervical squamous cell carcinoma (n = 7) and endometrial adenocarcinoma (n = 11) were examined. Immunoreactivity was semi-quantitatively evaluated as negative (0, < 5% of cells stained), focally positive (1+, 5-10% of cells stained), positive (2+, 11-50% of cells stained) or diffusely positive (3+, > 50% of cells stained). Staining intensity for each subtype was graded from 0 to 3 and a mean intensity was calculated.</p> <p>Results</p> <p>Eighty percent of PSTT (12/15) were immunoreactive for GPC3 (0, 20; 1+, 20%; 2+, 40%; 3+, 20%) with a mean intensity of 1.3. Stronger, predominately cytoplasmic staining was seen in larger multi- and mononucleated cells with smaller mononucleate cells showing weak muddy cytoplasmic staining. Both PSN cases were positive (1+, 50%; 2+, 50%) and two of nine invasive cervical squamous cell carcinomas showed staining (0, 57%; 1+, 29%; 2+, 14%), predominately in a basal distribution. Other uterine tumors and non-neoplastic tissues were negative.</p> <p>Conclusions</p> <p>Identification of GPC3 in PSTT and PSN is consistent with the derivation of these lesions from intermediate trophoblasts, which have been described to express GPC3. GPC3 may be a useful adjunct immunohistochemical marker in differentiating PSTT from non-trophoblastic tumors.</p

    Investigating the Impacts of Recommendation Agents on Impulsive Purchase Behaviour

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    The usage of recommendation agents (RAs) in the online marketplace can help consumers to locate their desired products. RAs can help consumers effectively obtain comprehensive product information and compare their candidate target products. As a result, RAs have affected consumers’ shopping behaviour. In this study, we investigate the usage and the influence of RAs in the online marketplace. Based on the Stimulus-Organism-Response (SOR) model, we propose that the stimulus of using RAs (informativeness, product search effectiveness and the lack of sociality stress) can affect consumers’ attitude (perceived control and satisfaction), which further affects their behavioural outcomes like impulsive purchase. We validate this research model with survey data from 157 users of RAs. The data largely support the proposed model and indicate that the RAs can significantly contribute to impulsive purchase behaviour in online marketplaces. Theoretical and practical contributions are discussed
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