Temporal dissipative solitons in the Morris-Lecar model with time-delayed feedback.

We study the dynamics and bifurcations of temporal dissipative solitons in an excitable system under time-delayed feedback. As a prototypical model displaying different types of excitability, we use the Morris-Lecar model. In the limit of large delay, soliton like solutions of delay-differential equations can be treated as homoclinic solutions of an equation with an advanced argument. Based on this, we use concepts of classical homoclinic bifurcation theory to study different types of pulse solutions and to explain their dependence on the system parameters. In particular, we show how a homoclinic orbit flip of a single-pulse soliton leads to the destabilization of equidistant multi-pulse solutions and to the emergence of stable pulse packages. It turns out that this transition is induced by a heteroclinic orbit flip in the system without feedback, which is related to the excitability properties of the Morris-Lecar model.

DFTB+, a software package for efficient approximate density functional theory based atomistic simulations.

DFTB+ is a versatile community developed open source software package offering fast and efficient methods for carrying out atomistic quantum mechanical simulations. By implementing various methods approximating density functional theory (DFT), such as the density functional based tight binding (DFTB) and the extended tight binding method, it enables simulations of large systems and long timescales with reasonable accuracy while being considerably faster for typical simulations than the respective ab initio methods. Based on the DFTB framework, it additionally offers approximated versions of various DFT extensions including hybrid functionals, time dependent formalism for treating excited systems, electron transport using non-equilibrium Green's functions, and many more. DFTB+ can be used as a user-friendly standalone application in addition to being embedded into other software packages as a library or acting as a calculation-server accessed by socket communication. We give an overview of the recently developed capabilities of the DFTB+ code, demonstrating with a few use case examples, discuss the strengths and weaknesses of the various features, and also discuss on-going developments and possible future perspectives.

Bias-induced conformational switching of supramolecular networks of trimesic acid at the solid-liquid interface.

Using the tip of a scanning tunneling microscope, an electric field-induced reversible phase transition between two planar porous structures ("chickenwire" and "flower") of trimesic acid was accomplished at the nonanoic acid/highly oriented pyrolytic graphite interface. The chickenwire structure was exclusively observed for negative sample bias, while for positive sample bias only the more densely packed flower structure was found. We suggest that the slightly negatively charged carboxyl groups of the trimesic acid molecule are the determining factor for this observation: their adsorption behavior varies with the sample bias and is thus responsible for the switching behavior.

From hydrogen bonding to metal coordination and back: Porphyrin-based networks on Ag(111).

The self-assembly of a metal-free porphyrin bearing two pyridyl coordinating sites and two pentyl chains at trans meso positions was investigated under ultrahigh vacuum on a Ag(111) surface by scanning tunneling microscopy (STM). The STM measurements revealed a well-ordered close-packed structure with a rhombic unit cell for coverages ≤1 monolayer with their molecular plane parallel to the surface. The growth direction of the molecular islands is aligned along the step edges, which are restructured due to molecule-substrate interactions. The shorter unit cell vector of the molecular superstructure follows the〈1-10〉direction of the Ag(111) substrate. Hydrogen bonds between pyridyl and pyrrole groups of neighboring molecules as well as weak van der Waals forces between the pentyl chains stabilize the superstructure. Deposition of cobalt atoms onto the close-packed structure at room temperature leads to the formation of a hexagonal porous network stabilized by metal-ligand bonding between the pyridyl ligands and the cobalt atoms. Thermal annealing of the Co-coordination network at temperatures >450 K results in the transformation of the hexagonal network into a second close-packed structure. Changes in the molecule-substrate interactions due to metalation of the porphyrin core with Co as well as intermolecular interactions can explain the observed structural transformations.

[Duodenal diverticulum--a therapeutic challenge]. / Blutendes Duodenaldivertikel - eine therapeutische Herausforderung.

We report the case of an 81-year-old women with a duodenal diverticular bleeding in the second portion of the duodenum. Various therapies are used to halt haemorrhaging in this tissue, including surgical or endoscopic intervention and transarterial embolisation. The lesion was identified and treated endoscopically with hypertonic saline solution and epinephrine. Because of a fistula and a continual bleeding we use a hemoclip two days later. The bleeding was completely controlled. However, a small mucosal defect was noted at the site where the hemoclip was applied, and an operation was necessary. Finally we discuss the therapy optoins based on a review of the literature.

Tumor promoter TPA mimics irradiation effects on the cell cycle of HeLa cells.

When asynchronous and synchronous HeLa cells were incubated with small doses (10(-7) M) of tumor promoter 12 O-tetradecanoylphorbol-13-acetate (TPA), a variety of transient alterations in the replication cycle were detected within 24 hours by the use of independent methods. Especially, a delayed passage through the S phase and influences on the G2 phase resemble x-ray irradiation effects on cell cultures. None of these alterations was observed with the hyperplasiogenic but nonpromoting 4-O-methyl-TPA.

Lens culinaris lectin immobilized on sepharose: binding and sugar-specific release of intact tissue culture cells.

Lens culinaris lectin (LCL) covalently linked to 2B Sepharose binds tissue culture cells to the matrix. This is prevented by hapten sugars specific for LCL. Unlike other immobilized lectins, lens culinaris lectin allows the removal of bound cells from the matrix on addition of the specific sugars in a concentration-dependent manner. Binding and release occur under physiological conditions. Released cells continue to grow.

Ab initio phase diagram of oxygen adsorption on W(110).

The phase diagram of oxygen adsorption on the W(110) surface is derived without any empirical parameters by a combination of density functional theory (DFT) calculations, the cluster expansion (CE) technique and Monte Carlo (MC) applications. Coverages up to 1 monolayer are considered corresponding to the range of oxygen concentrations, 0≤x(O)≤1. DFT results for single-site adsorption and in particular for full coverage reveal that adsorption at threefold hollow (H3) sites is by far the most stable one. Therefore, the CE is done for an atomic layer with the two H3 sublattices of the W(110) surface. Based on 60 DFT calculations with fully relaxed atomic geometries of lateral unit cells containing 12 atoms, and a ground state search for 80 394 structures, four ground state structures are found with the lateral unit cells (2 × 5) for x(O) = 0.20, (2 × 2) (a) for x(O) = 0.25, (2 × 1) for x(O) = 0.50 and (2 × 2) (b) for x(O) = 0.75. In agreement with experiments the most stable structures are (2 × 1) and (2 × 2) (b), which correspond to higher coverages. The thermodynamical stability of the two ground states at lower coverages is very weak. Detailed analysis of the relaxation of the (2 × 1) structure reveals sizeable lateral stresses acting on the surface tungsten atoms. On the basis of the effective cluster interactions MC simulations are performed in order to derive the critical temperatures by which the phase diagram is finally constructed.

Dynamic regimes of buoyancy-affected two-phase flow in unconsolidated porous media.

The invasion and subsequent flow of a nonwetting fluid (NWF) in a three-dimensional, unconsolidated porous medium saturated with a wetting fluid of higher density and viscosity have been studied experimentally using a light-transmission technique. Distinct dynamic regimes have been found for different relative magnitudes of viscous, capillary, and gravity forces. It is shown that the ratio of viscous and hydrostatic pressure gradients can be used as a relevant dimensionless number K for the characterization of the different flow regimes. For low values of K, the invasion is characterized by the migration and fragmentation of isolated clusters of the NWF resulting from the prevalence of gravity and capillary forces. At high values of K, the dominance of viscous and gravity forces leads to an anisotropic fingerlike invasion. When the invasion stops after the breakthrough of the NWF at the open upper boundary, the invasion structure retracts under the influence of gravity and transforms into stable vertical channels. It is shown that the stability of these channels is the result of a balance between hydrostatic and viscous pressure gradients.

Inheritance of immunogenicity and metastatic potential in murine cell hybrids from the T-lymphoma ESb08 and normal spleen lymphocytes.

T-lymphoma cells were fused with normal lymphoid cells to examine the segregation of tumorigenicity and metastatic capacity in the hybrids. In independent fusions the immunogenic ESb08 T-lymphoma line fused successfully with normal syngeneic spleen cells (from DBA/2 and CD1 mice) enriched either with T-cells or B-cells. Ten times fewer hybrids were obtained with B-cells compared to the number obtained with T-cells, and marker assays showed that both types of fusions preferentially generated T-T hybridomas. Some of the hybrids resembled their tumor parent in their ability to form primary and secondary tumors only in irradiated DBA/2 mice, whereas other hybrids lost the high ESb08 immunogenicity, were equally tumorigenic, and in some cases metastatic, in nonirradiated mice. DNA distributions of the original hybrid lines ranged from a hexaploid DNA content (expected for complete hybrids derived from a tetraploid line and normal diploid cells) to a tetraploid DNA content, confirming the reported chromosome instability of T-T hybrids. No correlation was noted between the initial DNA content and tumorigenicity, but in the case of complete hybrids, reduction in the ploidy levels always was observed in the cells of primary and metastatic lesions. One chromosomally stable and highly malignant hybrid (C2), which was analyzed for segregation of chromosomes and for drug-resistance markers, showed preferential loss of chromosomes from the normal T-cell fusion partner. The decreased immunogenicity of this hybrid could not be related to any detectable loss of chromosomes from the ESb08 tumor parent.

Early effects of the tumor-promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate on the cell cycle traverse of asynchronous HeLa cells.

Within 24 hr after incubation of synchronous HeLa cell cultures with small nontoxic doses of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA; 10(-7) or 10(-8) M), a variety of transient alterations in the cell cycle traverse was detected by different techniques. The measurement of thymidine incorporation rates into DNA, of labeling and mitotic indices, and of flow cytometry revealed (a) an inhibition of cells in G1 shortly prior to their entering S phase, (b) a reduced rate of DNA synthesis and a delayed passage of cells through S phase which were in this phase on addition of TPA, (c) a delayed passage through G2 of a portion of cells which were somewhere in the first half of the S phase on addition of TPA, and (d) an instant but short-lasting blockage in G2 immediately before mitosis. The effects of TPA are reminiscent of published results on X-irradiated cell cultures. None of these effects was noticed with the hyperplasiogenic but nonpromoting phorbol ester 4-O-methyl-12-O-tetradecanoylphorbol-13-acetate (10(-6) M). The data were confirmed by experiments with synchronized HeLa cells as described in an accompanying paper.

Responses of synchronized HeLa cells to the tumor-promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate as evaluated by flow cytometry.

A flow cytometric study was carried out on the effects of tumor-promoting 12-O-tetradecanoylphorbol-13-acetate (TPA; 10(-8) M) on HeLa cells synchronized by amethopterin for DNA synthesis. Cells treated with TPA at the time of release from the amethopterin block showed a delayed passage through S phase and partially through G2 in their immediate life span as measured 24 hr after release. This late G2 delay was not observed when TPA was added to cells during late S or G2 phase. In this case, however, a direct inhibition of cells in G2 became evident as observed about 15 hr after release from block. None of these effects was caused by the nonpromoting 4-O-methyl-12-O-tetradecanoylphorbol-13-acetate (10(-6) M). These data support observations obtained with asynchronous cultures. The TPA effects resemble those reported after X-irradiation of cell cultures.

Sensitization of multidrug-resistant mouse ascites HD33 and Chinese hamster ovary CHRC5S3 cells by a photoreactive vinblastine derivative, NAPAVIN.

We have synthesized a new photoreactive vinblastine derivative, 3-[[[2-amino(4-azido-2-nitrophenyl)ethyl]amino] carbonyl]-O4-deacetyl-3-de-(methoxycarbonyl)-vincaleukoblastine (NAPAVIN), which absorbs light at around 450 nm. We report here its effects in vitro on multidrug-resistant mouse HD33 Ehrlich-Lettré ascites cells, on Chinese hamster ovary CHRC5S3 cells, on the corresponding drug-sensitive cells, on chemosensitive rat TMA1 mammary carcinoma, and on human SW48 colon carcinoma cells. Cells were incubated with the drug prior to activation by laser light at 457 nm. In Vinca alkaloid-sensitive cells, the short-term effects (30 to 72 h after treatment) of NAPAVIN with and without irradiation on cell proliferation are comparable to those of vinblastine. In drug-resistant cells, NAPAVIN without irradiation reduces the 50% inhibitory concentration 2- to 9-fold, compared with vinblastine. Upon irradiation with an argon laser at 457 nm, the concentration causing 50% inhibition of cell proliferation is further decreased to a total of 9- to 33-fold. Long-term effects (up to 6 wk after treatment) are seen in both sensitive and resistant cells. A single dose of the photoactivated drug causes a 6- to 9-fold larger delay (5 wk) in proliferation, compared with an equal dose of vinblastine.

Conditional expression of N-myc in human neuroblastoma cells increases expression of alpha-prothymosin and ornithine decarboxylase and accelerates progression into S-phase early after mitogenic stimulation of quiescent cells.

To elucidate the contribution of the N-Myc protein to neuroblastomas we have used a synthetic inducible expression system on the basis of the tetracycline repressor of E coli to reversibly express N-myc in a human neuroblastoma cell line in which expression of endogenous N-myc is barely detectable. Like the c-Myc protein, N-Myc up-regulates the expression of both alpha-prothymosin and ornithine decarboxylase. Induction of N-myc increases both the rate of DNA-synthesis and the proliferation rate, and shortens the G1 phase of the cell cycle. A comparison of cell populations in which the presence of N-Myc protein was restricted to different parts of G(zero)/G1 revealed that N-Myc is rate-limiting for cell cycle progression during the first 5 h after serum stimulation of quiescent cells providing direct evidence that Myc-proteins act early after mitogenic stimulation of quiescent cells.

Selective alteration of erythrocyte deformabiliby by SH-reagents: evidence for an involvement of spectrin in membrane shear elasticity.

In order to elucidate the molecular basis of membrane shear elasticity, the effect of membrane protein modification by SH-reaents on the deformability of human erythrocytes was studied. Deformability was quuantified by measuring the elongation of erythrocytes subjected to viscometric flow in a transparent cone plate viscometer. Impermeable SH-reagents proved to have no mechanical effect. Many, but not all, permeable SH-reagents markedly decreased the elongation. Among these, bifunctional SH-reagents (e.g. diamide, tetrathionate and N, N' -p-phenylenedimaleimide) able to cross-link membrane SH-groups were more effective than monofunctional SH-reagents (e.g. N-ethylmaleimide and ethacrynic acid). The bifunctional SH-reagents produced a 50% decrease of elongation after modification of less than 5% of the membrane SH-groups. In contrast, for a comparable effect, more than 20% of the SH-groups had to be modified by the monofunctional reagents. The effect of SH-oxidizing agents was fully reversible after treatment with disulfide-reducing agents. All bifunctional SH-reagents induced a dimerization of a small fraction of spectrin. Anaalysis of the distribution of the diamide-induced disulfide bonds among the various membrane protein fractions showed that this agent preferentially acts on the spectrin polypeptides. The results provide direct experimental evidence that the native arrangement of spectrin is essential for the shear resistance of the erythrocyte membrane and that introduction of small numbers of intermolecular cross-links as well as modification within the molecule lead to a rapid loss of this function.

Biphasic effect of protein kinase C activators on spontaneous and glucocorticoid-induced apoptosis in primary mouse thymocytes.

Spontaneous and glucocorticoid (fluocinolone acetonide, FA)-induced apoptosis of primary mouse thymocytes was inhibited by protein kinase C (PKC) activators such as bryostatin-1 and phorbol ester 12-O-tetradecanoyl-phorbol-13 acetate (TPA) within the first 2-4 h of incubation but was enhanced upon prolonged treatment. Only the anti-apoptotic but not the pro-apoptotic effect of TPA was completely suppressed by the PKC inhibitor Goe 6983 and moderately inhibited by Goe 6976. Immunoblot analysis revealed distinct PKC alpha, beta, delta, eta, theta, mu and zeta signals, a very faint PKCepsilon and no PKCgamma signal. Upon prolonged TPA treatment all PKC isoenzymes became downregulated, albeit at different rates (PKCdelta>alpha>mu>beta,theta>>eta,zeta). No significant generation of caspase-derived catalytic PKC fragments, as found to be produced upon induction of apoptosis and to be pro-apoptotic in other systems, was observed in FA- or TPA-treated thymocytes. It is concluded that the early anti-apoptotic effect of TPA depends on the activation of n-type PKC isoenzymes, whereas stimulation of spontaneous and FA-induced apoptosis by TPA ensues, at least partially, from a downregulation (or inactivation) of anti-apoptotic PKC species, i.e. in primary thymocytes PKC activation is primarily involved in a negative regulation of apoptosis.

In vitro and clinical characterisation of a Newcastle disease virus-modified autologous tumour cell vaccine for treatment of colorectal cancer patients.

A virus-modified autologous tumour cell vaccine prepared from human colorectal cancer cells is described. After dissociation an average of 5 x 10(7) cells/g tissue were obtained from primary tumours and 9 x 10(7)/g tissue from metastases with an average viability of 72% and 51%, respectively. Following irradiation (200 Gy), inactivation of the proliferative activity of the cells was demonstrated by their degeneration in tissue culture and the absence of incorporation of 3H-labelled thymidine. One third of the cells were still metabolically active, as shown by the incorporation of 3H-uridine and a mixture of 3H-aminoacids. The dissociated cells expressed MHC class I and II antigens in a qualitatively similar way to tissue sections. Epithelium-specific antigens (detected by MAb HEA125) were expressed on an average of more than 75% cells of the suspension, while leucocyte-specific antigens (detected by MAb CD53) were expressed on an average of less than 25% cells. The vaccine was prepared by admixing the nonlytic strain Ulster of Newcastle disease virus (NDV) with the tumour cell suspension. The NDV adsorption at tumour cells was shown by electron microscopy. Clinically, the treatment with the vaccine was associated with an increased sensibilisation against autologous tumour cells, measured by DTH skin reactivity. First results in 23 patients with colorectal liver metastases who underwent "curative" liver resection followed by vaccination show a clear correlation between the induced increase of DTH skin reaction against autologous tumour cells and the recurrence-free interval. No correlation was found for DTH reaction caused by standard antigens (Mérieux test), NDV alone or autologous normal liver tissue. The results demonstrate the possibility of preparing immunogenic virus-modified autologous tumour cell vaccine from colorectal cancer tissue, which could be used for cancer therapy.

The Heidelberg flow analyzer and sorter (HEIFAS) approach on the prescreening of uterine cancer.

A dual laser flow system has been proved and used with a novel staining method for simultaneous quantitative DNA and protein analysis. A diamidinophenylindole compound (DAPI) for DNA has been employed in combination with sulforhodamine (SR 101) for protein. With this dye mixture various cell types of the cervical smear could be identified. Despite some overlapping, clusters of leukocytes, endocervicals, (para)basals, intermediates, superficials and dys/neoplastic cells together with artificial events could be discriminated. Up to now the problem of negative cells which create positive signals (false alarms) in the dys/neoplastic region could not be sufficiently solved.

Visualization of multidimensional spectra in flow cytometry.

Flow data from a cell sorter have been processed by hardwired circuits which include amplification, discrimination, coincidence requirements, peak sensing and holding, A-D conversion, and a computerized pulse height analysis with storage of the spectra obtained. Two dimensional spectra can be stored directly in memory, on tape and disk. Three and four parametric cellular events can be recorded on line during the flow measurement in a sequential mode on tape for subsequent recall. Simple processing of these data can be performed for displaying of two dimensional projections from these multidimensional spaces based on threshold conditions for the remaining parameters. Interfaced transmission of the stored data to a large scale computer enables more sophisticated data analysis. Data reduction by means of a multidimensional probability analysis has been carried out in order to transfer the spectra to a computerized picture system for display. This system creates perspective two-dimensional images from a three-dimensional data space. Frequency can be converted into grey levels. Hard copy in color (color as the third dimension and color intensity as frequency) simplifies the visualization of multiparametric flow data sets.