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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1573-4951
    Keywords: Molecular dynamics ; Nematic liquid crystal ; Smectic liquid crystal ; Columnar liquid crystal ; Molecular modelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary We review recent progress in the computer simulation of liquid crystals, with special emphasis on hard particle models. Surprisingly, the simplest molecular models, taking account only of molecular size and shape, are sufficient to generate a wide variety of liquid crystalline phases, closely analogous to those observed in real life. Thermodynamic stability of different phases is very sensitive to shape, and presumably will also be sensitive to further details of intermolecular interactions as they are incorporated into the model. Realistic atom-atom potential models of liquid crystals are available, but the associated simulations are quite expensive. Thus, while idealized models may be used to study quite general, fundamental properties of mesophases, the modelling of specific liquid crystal systems in a realistic way remains a great challenge. Progress continues to be made on both these fronts.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1437-1596
    Keywords: Mitochondrial DNA ; Forensics ; Hair ; Human polymorphisms ; Sequencing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Law
    Notes: Abstract Two sets of studies were performed to evaluate the forensic utility of sequencing human mitochondrial DNA (mtDNA) derived from various tissues and amplified by the polymerase chain reaction (PCR). Sequencing was performed on a Perkin-Elmer/Applied Biosystems Division (PE/ABD) automated DNA sequencer (model 373A). The first set of experiments included typical validation studies that had previously been conducted on forensic DNA markers, such as: chemical contaminant effects on DNA from blood and semen and the effect of typing DNA extracted from body fluid samples deposited on various substrates. A second set of experiments was performed strictly on human hair shafts. These studies included typing mtDNA from hairs that were: (1) from different body areas, (2) chemically treated, (3) from deceased individuals, and (4) deliberately contaminated with various body fluids. The data confirm that PCR-based mtDNA typing by direct automated sequencing is a valid and reliable means of forensic identification.
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  • 3
    ISSN: 1437-1596
    Keywords: DNA ; PCR ; Sequential multiplex amplification (SMA) ; STR ; Forensic ; DNA ; PCR ; sequentielle multiplex Amplifikation (SMA) ; STR ; Forensik
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Law
    Description / Table of Contents: Zusammenfassung Die Methode der sequentiellen multiplex Amplifikation (SMA) ermöglicht die Wiederverwendung einer limitierten Menge genomischer DNA für mehrere aufeinanderfolgende PCR Amplifikationen. Die Isolierung genomischer DNA aus den PCR-amplifizierten Proben erfolgte durch Mikrofiltration. 5 ng genomischer DNA wurden als Ausgangsmenge eingesetzt und bis zu 5 verschiedene Loci in getrennten PCR-Ansätzen nacheinander untersucht. Die Amplifikationsmuster der sequentiellen multiplex Amplifikation wurden mit denen aus individuellen Amplifikationen verglichen und waren identisch. Diese Technik ermöglicht die Untersuchung verschiedener Loci ausgehend von einer begrenzten Menge an genomischer DNA und kann daher besonders Anwendung finden, wenn geringe Mengen an genomischer DNA für die PCR Amplifikation zur Verfügung stehen.
    Notes: Abstract A method called Sequential Multiplex Amplification (SMA) has been developed whereby a limited amount of DNA extracted from a sample can be reutilized for several single polymerase chain reaction (PCR) amplifications. The method involves recovery of genomic template DNA by microfiltration of PCR-amplified samples. Up to 5 different loci have been typed, each in a single system PCR-based assay, beginning with a test quantity of 5 ng template DNA. Genotypes of the DNA donors were compared with those obtained from individual amplifications and shown to be identical. This could be a useful technique for typing a number of loci from a limited amount of DNa and to recover template DNA from samples previously subjected to PCR. Obviously, when small quantities of template DNA are available, this technique can prove quite useful.
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  • 4
    ISSN: 1619-7089
    Keywords: Radioimmunoscintigraphy ; Antibody localisation ; Circulating antigen ; Rat model ; Immune complex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effect of circulating antigen (human kappa light chains (LC)) on radioimmunoscintigraphy was examined in a normal rat model. Rats were implanted subcutaneously with kappa (test) and lambda (control) LC coupled to sepharose beads (500 μg LC/ml swollen gel). When 131I-labelled monoclonal antibody, K-1-21 was injected, clear images of specific antibody localisation to the kappa implant were seen 6 days later. The kappa implant: blood ratio (K:B) was 7.69±0.45, which represented an implant uptake of 2.52±0.20 percent injected dose per gram (%ID/g). When 131I-K-1-21 was preincubated with 125I-kappa LC at ratios of up to 1:10 antibody: antigen, (w/w) before injection; or if antigen was given daily by bolus injection or continuously infused via an osmotic pump, very clear specific images of antibody localisation to the kappa implant were still obtained. There was, however, a decline in the absolute uptake of label by the kappa implant. The greatest change was observed following continuous antigen infusion, when kappa implant uptake fell to 1.26±0.1 %ID/g. Nevertheless, the K:B ratio was still maintained at 6.8±0.2, due to increased clearance of antibody from the blood. Thus, in this case, where antigen and antibody might be expected to form small, soluble immune complexes, there was no major deleterious effect on radioimmunoscintigraphy.
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  • 5
    ISSN: 0173-0835
    Keywords: Capillary electrophoresis ; DNA ; Mitochondrial DNA ; Forensic DNA typing ; Polymerase chain reaction analysis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: The polymorphic control region of mitochondrial DNA (mtDNA) is becoming more commonly used in forensic applications to differentiate among individuals in a population. Two hypervariable regions (HV1 and HV2) are often sequenced following amplification of the mtDNA via the polymerase chain reaction (PCR). More rapid screening assays would reduce both the effort and the expenses of comparing two samples. A methodology has been developed that first uses restriction endonuclease digestion of the PCR-amplified mtDNA using RsaI and Mn/I and then capillary electrophoresis (CE) to separate and size the PCR-RFLP fragments. This rapid procedure offers an alternative method for screening of polymorphisms in amplified mtDNA samples. In addition, the presence of a T→C transition at position 16189, which gives rise to the so-called “C-stretch” in HV1, may be predicted from the presence of nonspecific PCR products in the CE results.
    Additional Material: 4 Ill.
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  • 6
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The implementation of parallel molecular dynamics techniques is discussed in the context of the simulation of single-site anisotropic potentials. We describe the use of both replicated data and domain decomposition approaches to molecular dynamics and present results for systems of up to 65536 Gay-Berne molecules on a range of parallel computers (Transtech i860/XP Paramid, Intel iPSC/860 Hypercube, Cray T3D). We find that excellent parallel speed-ups are possible for both techniques, with the domain decomposition method found to be the most efficient for the largest systems studied. © 1997 by John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 1560-1564 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The helical twisting power βM determines the pitch of the chiral nematic phase produced when a nematic liquid crystal is doped with a low concentration of chiral solute molecules. Molecules with large βM values have potential applications in electro-optic displays and in optical data storage. This paper describes a new simulation technique which allows the prediction of both the sign and magnitude of βM. The method employs Monte Carlo simulations of a fully atomistic model of a chiral dopant in the presence of a twisted nematic solvent composed of Gay–Berne particles. Calculations are presented for five different chiral dopants, with results that are in good agreement with existing experimental data. © 2000 American Institute of Physics.
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  • 8
    ISSN: 1437-1596
    Keywords: DNA ; VNTR ; STR ; PAGE ; Composite gels ; DNA ; VNTR ; STR ; PAGE ; zusammengesetzte Gele
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Law
    Description / Table of Contents: Zusammenfassung Die genetische Typisierung von Short Tandem Repeat (STR)-Loci erfordert elektrophoretische Trenntechniken, welche in Abhängigkeit vom Locus Allele unterscheiden können, welche sich in der Größe durch nur 2, 3 oder 4 Basenpaare unterscheiden. Zahlreiche solcher Loci können mit Hilfe der horizontalen, diskontinuierlichen Polyacrylamidgel-Elektrophorese (hd-PAGE) aufgetrennt werden. Einige Loci stellen jedoch eine besondere Herausforderung an die Trenntechnik. Ein zusammengesetztes (oder Schritt-)Gelsystem, welches aus zwei Zonen besteht - einer anodischen und einer kathodischen -, welche sich durch die Porengröße und Ionenstärke unterscheiden, wurde entwickelt, um die Auftrennung von DNA-Fragmenten zu verbessern, ohne daß eine zusätzliche elektrophoretische Ausstattung erforderlich ist. In Abhängigkeit von der Porengröße und von der Ionenstärke kann die anfängliche Wanderungsgeschwindigkeit verstärkt oder verlangsamt werden, mit Auswirkung auf die Auflösung. Im Vergleich zur hd-PAGE kann dieses zusammengesetzte gelelektrophoretische System zu einer gesteigerten Ruftrennung von PCR-amplifizierten STR-Allelen führen.
    Notes: Summary Genetic typing of short tandem repeat (STR) loci may require electrophoretic separation techniques which, depending on the locus, can resolve alleles differing in size by only 2, 3 or 4 base pairs (bps). Many such loci can be separated by horizontal, discontinuous polyacrylamide gel electrophoresis (hd-PAGE). However, some loci present particular separation challenges. A composite (or step) gel system consisting of 2 zones, anodal and cathodal, which differ by pore size and ionic strength, has been developed to augment resolution of DNA fragments without a need for additional electrophoretic equipment. Depending on pore size, as well as ionic strength, initial migration can be increased or decreased to effect resolution. When compared with hd-PAGE, this composite gel electrophoretic system can result in enhanced resolution of PCR amplified STR alleles.
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  • 9
    ISSN: 1546-1718
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] The rate and pattern of sequence substitutions in the mitochondrial DNA (mtDNA) control region (CR) is of central importance to studies of human evolution and to forensic identity testing. Here, we report a direct measurement of the intergenerational substitution rate in the human CR. We compared ...
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 8654-8663 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamics simulations are described for liquid crystal molecules composed of two Gay-Berne particles connected by an eight-site Lennard-Jones alkyl chain. Calculations have been carried out for 512 molecules in the NVE and NPT ensembles for simulation times of up to 6.4 ns. The system exhibits the sequence of phases: isotropic liquid, smectic-A, smectic-B, and the simulations demonstrate the spontaneous growth of a smectic-A liquid crystal over a period of approximately 6 ns on cooling from the isotropic liquid. Model molecules are seen to remain flexible and able to change conformation in the smectic-A phase. As temperature is reduced molecules become elongated as the number of gauche conformations drops, leading to a small increase in the spacing of smectic layers. The latter is seen through the temperature dependence of the Gay-Berne radial distribution function resolved parallel to the direction of orientational order. Results are presented which show an odd–even variation of orientational order parameters for bonds in the alkyl chain, and a change in effective torsional potentials as the system is cooled from isotropic liquid to a smectic-A phase. © 1997 American Institute of Physics.
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