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  • Springer  (17)
  • BMJ Publishing  (3)
  • 1
    ISSN: 1572-817X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract The propagation of ultrashort optical pulses in semiconductor-doped glass waveguides is investigated theoretically for wavelengths below the half bandgap. The linear and non-linear properties of the composites are obtained and a field equation for pulse propagation is derived. This equation yields a new family of sub-picosecond optical solitons which are observed in numerical simulations. Interesting applications are anticipated for ultrafast all-optical signal processing.
    Materialart: Digitale Medien
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Adsorption 1 (1995), S. 17-27 
    ISSN: 1572-8757
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Physik , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Abstract A two-dimensional model is developed to describe the hydrodynamics, heat transfer and adsorption phenomena associated with the adsorptive storage of natural gas (NG) in cylindrical reservoirs. Intraparticle and film resistances to both heat and mass transfer are neglected. In the momentum equation, Ergun's law is considered locally valid and is extended to two dimensions. These assumptions are fully justified in the paper. Numerical results are presented concerning the pressurization and blowdown of an ultra-lightweight 50 litre cylinder, commercially available for the storage of compressed NG, if it were filled with an activated carbon having a good adsorptive storage capacity. A simple formula is also proposed to predict the filling times for fast charges. The predicted temperature changes in the packed-bed are in good agreement with those reported in the literature for an experimental charge/discharge.
    Materialart: Digitale Medien
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
    ISSN: 1572-8757
    Schlagwort(e): methane adsorption ; on-board storage ; mathematical modeling ; numerical simulation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Physik , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Abstract The charge of natural gas adsorption storage systems is studied numerically, With emphasis given to the impact on its dynamics of intraparticle diffusional resistances to mass transport. Besides adsorption kinetics and thermal effects, the simulation model takes into account both mass transport inside the adsorbent and hydrodynamics of flow through the packed bed. Numerical results are presented for change with methane of a 50 liter cylindrical reservoir, filled with hypothetical adsorbents with diffusional time constants in the range 10−3 s1 D/R p 2 ≤ ∞. and with the adsorption equilibrium curve of a commercially available activated carbon with a good adsorptive storage capacity. An attempt is made to assemble the charge histories for different values ofD/R p 2 , in a single cure by using a modilied time scale.
    Materialart: Digitale Medien
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 4
    ISSN: 1248-9204
    Schlagwort(e): Inguinal hernia ; Colonic neoplasms ; Polypropylene mesh
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary There seems to be an association between inguinal hernias and colon cancer, but to date no causal relation has been reported, despite the great number of papers evaluating the role of sigmoidoscopy and barium enema in hernia patients. The authors present three cases of elderly patients with inguinal hernia and cancer of the sigmoid colon. All patients had a long standing inguinal hernia and a clinical history suggesting colonic malignancy which was confirmed on barium enema. One patient had a sigmoid tumor incarcerated in a huge scrotal hernia. The patients were treated by tumor resection with primary anastomosis and a simultaneous hernia repair by the Stoppa technique, with pre-peritoneal polypropylene mesh. No morbidity arose from this treatment policy. We therefore conclude that the association between colon cancer and inguinal hernia is mainly coincidental, and the cancer must be suspected on a clinical basis. The use of synthetic mesh in association with colonic resection did not lead to post operative infection, allowing concomitant treatment of both diseases in elderly, high risk patients.
    Materialart: Digitale Medien
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 5
    ISSN: 1248-9204
    Schlagwort(e): Femoral hernia ; Biometry ; Anatomy ; Etiology
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The possibility of a biometric explanation for the genesis of femoral hernia has motivated several studies on the anatomy and dimensions of the femoral canal. However, because of methodologic flaws, there is still a lack of consistent results regarding this matter. The aim of this paper was to improve the understanding of the biometry of the femoral ring and canal and development of femoral hernia by a preperitoneal access. The longitudinal and transverse diameters and the depth of the femoral canal were measured in 50 male cadavers between 22 and 76 years of age. A great variability of diameters was found, and the right longitudinal and transverse diameters (1.65 ± 0.28 and 1.71 ± 0.37 cm) were significantly larger than the left (1.53 ± 0.26 and 1.53 ± 0.34 cm); p=0.021 and p=0.013, respectively. However, the depth of the left femoral canal (1.60 ± 0.41 cm) was significantly larger than the right (1.40 ± 0.38 cm); p=0.011. The wider femoral ring could explain the higher incidence of right femoral hernias. On the other hand, the great variability of diameters found, as large as 2.58 cm with the absence of femoral hernia, indicates that femoral ring diameter is not the only factor involved in the etiology of femoral hernia. We conclude that widened dimensions of the femoral ring alone are not a sufficient condition for the genesis of femoral hernias, but play a role in their formation, explaining their higher incidence in the right groin.
    Materialart: Digitale Medien
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Bulletin of environmental contamination and toxicology 57 (1996), S. 47 -53 
    ISSN: 1432-0800
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik , Medizin
    Materialart: Digitale Medien
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Bioprocess and biosystems engineering 12 (1995), S. 187-192 
    ISSN: 1432-0797
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Abstract Modeling of biofilm reactors has been carried out by several authors. Most of the models use first-order or zero-order kinetics, because of the simplicity of the solution of the mathematical problem. However, the reaction kinetics for many practical situations is a non-linear Monod kinetics, which requires numerical solutions. This paper deals with the modeling of biofilm reactors and effectiveness factor calculations for a biofilm particle with Monod kinetics and two consecutive reactions. The model is applied to biological denitrification in a fluidized bed bioreactor, in which the liquid phase is assumed to be in plug flow. Effectiveness factors of biofilm are numerically calculated by solving the system of ODES by orthogonal collocation. Axial concentration profiles of nitrate and nitrite species are calculated and compared with experimental results.
    Materialart: Digitale Medien
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Il nuovo cimento della Società Italiana di Fisica 7 (1986), S. 528-538 
    ISSN: 0392-6737
    Schlagwort(e): Magnetic films and plates
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Beschreibung / Inhaltsverzeichnis: Riassunto La magnetizzazione di superficie e la concentrazione di elettroni sono calcolati per modello a legame forte ed a orbitale singolo di metallo di transizione nell’approssimazione di Hartree-Fock, per una superficie (111) sella struttura f.c.c. ed una superficie (100) nella struttura s.c. Funzioni locali di Green nel piano di superficie e nel volume sono espresse come frazioni continue attraverso l’approccio di trasferimento di matrice. L’autoconsistenza piú i vincoli di neutralità di carica locale, uguagliznza di superficie e potenziali chimici di volume, determianosU s intraatomico di superficie di Hubbard e lo slittamento Δε degli orbitali di superficie. Le equazioni autoconsistenti sono state risolte graficamente facendo ricorso alla densità integrata di stati per volume of superficie. Il metodo è applicato a sistemi con parametri adeguati per Ni e Fe.
    Kurzfassung: Резюме Вычисляются поверхностная намагниченность и концентрация электронов в приближении Хартри-Фока для модели переходных металлов, в которой рассматривается сильная связь и единственная орбиталь. Вычисления проводятся для поверхности (111) B f.c.c. структуре и поверхности (100) B s.c. структуре. Локальные функции Грина на поверхностной плоскости и в объсме выражаются в виде непрерывных дробеи, используя подход матрицы переноса. Самосогласованность плюс ограничения локальной зарядовой нейтральности и равенство поверхностного и объемного химических потенциалов определяют поверхностный мезатомныйU s Хаббарда и химический сдвиг Δε поверхностных орбиталей. Самосогласованные уравнения решаются графически, используя интегрированную плотность состояний для объема или поверхности. Предложенный метод применяется к системам с параметрами, адекватными для Ni и Fe.
    Notizen: Summary The surface magnetization and electron concentration are calculated for a tight-binding, single-orbital model of a transition metal in the Hartree-Fock approximation, for a (111) surface in the f.c.c. structure and a (100) surface in a s.c. one. Local Green’s functions at the surface plane and in the bulk are expressed as continued fractions through the transfer matrix approach. Self-consistency plus constraints of local charge neutrality and equality of surface and bulk chemical potentials determine the surface intra-atomic HubbardU s and chemical shift Δε of surface orbitals. The self-consistent equations were solved graphically by recourse to the integrated density of states for bulk or surface. The method is applied to systems with parameters adequate for Ni and Fe.
    Materialart: Digitale Medien
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 9
    ISSN: 1573-2932
    Schlagwort(e): elemental composition ; fine sediments ; Tagus ; Atlantic shelf ; sediment transport ; pollution
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: Abstract The Tagus estuary, located at the western Iberian coast in front of Lisbon is the largest one in Portugal, where it drains highly populated and industrialised regions. The amount of sediment transported by this river is so great that the submarine delta is one of the largest in the Iberian margin, very well defined and reaching the 70m isobath. The geochemical pattern of the muddy deposit off the Tagus river has been determined by elemental analyses of bulk surficial sediments, collected at the Portuguese margin adjacent to the Tagus estuary. Measurements were carried out by energy-dispersive X-ray fluorescence spectrometry (EDXRF). Sediments were usually composed of fine particles (silts and clays) and were high in organic matter (measured as loss on ignition). Elemental concentrations for Zn and Pb clearly indicate an estuarine contamination probably associated with discharges from urban centers or due to the influence of the industries located downstream. Apparently the depletion on the Cu contents is caused by its release (soluble complexes) into the marine environment. Variations observed in the elemental distribution of the sediments off the Tagus with distance from the estuary seem to be dependent on the grain size distribution related to the dynamics of the sediment transport.
    Materialart: Digitale Medien
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 10
    ISSN: 1432-2277
    Schlagwort(e): Key words Hepatitis C virus ; Kidney transplantation ; Anti-thymocyte globulin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Hepatitis C virus (HCV) exhibits a dramatic genetic variability and several mechanisms of immunological response are unable to control hepatic and extrahepatic replication. Genotype 1 b is associated with more severe clinical manifestations and is less responsive to interferon. In addition, we have reported an increase of HCV RNA viral load after renal transplantation. Anti-thymocyte globulin (ATG) is supposed to increase viral replication and liver dysfunction in chronically infected renal graft recipients. We evaluated the genotype profile in HCV + patients of our Renal Transplant Unit and studied the effects of ATG, as part of the induction of immunosuppression, on viral load and liver enzymes abnormalities. From 726 renal graft recipients, 104 patients, with a mean follow up of 3.9 ± 2.9 years, were anti-HCV + by ELISA II. HCV RNA was measured by quantitative PCR. We correlated the viral load and biochemical liver parameters with genotype, exposure to ATG as induction therapy, early acute rejection episode and the duration of infection. Of the 81 patients tested, 72 % were viraemic and genotype 1 b was the predominant viral strain (66 %). The majority of these patients (65 %) were coinfected by two or more strains.There was no correlation between HCV RNA blood levels and liver enzymes. We did not find higher viral load with genotype 1 b infection (68 ± 88 mEq/ml vs 75.8 ± 123 mEq/ml in the others) nor with ATG induction therapy (43.5 ± 71.3 mEq/ml vs 64.1 ± 110.5 mEq/ml). Early acute rejection and longer follow up were not associated with higher levels of HCV RNA. The biochemical liver profile showed no relationship with the variables studied. We concluded that genotype 1 b is the predominant strain in our HCV + population and there is a great prevalence of coinfection with several genotypes. Our results did not confirm a deleterious effect of the use of ATG as induction therapy in these HCV-infected patients. Prospective randomised studies with liver biopsy evaluation are needed to answer more fully the remaining questions about the best immunosuppressive therapy in renal graft recipients with chronic HCV infection.
    Materialart: Digitale Medien
    Standort Signatur Einschränkungen Verfügbarkeit
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