534 research outputs found
Well-tempered n-plet dark matter
We study simple effective models of fermionic WIMP dark matter, where the
dark matter candidate is a mixture of a Standard Model singlet and an n-plet of
SU(2) with n >= 3, stabilized by a discrete symmetry. The dark matter mass is
assumed to be around the electroweak scale, and the mixing is generated by
higher-dimensional operators, with a cutoff scale > 1 TeV. For appropriate
values of the mass parameters and the mixing we find that the observed dark
matter relic density can be generated by coannihilation. Direct detection
experiments have already excluded large parts of the parameter space, and the
next-generation experiments will further constrain these models.Comment: 25 pages, 7 figures; v2: references and plots updated, minor
corrections, conclusions unchange
Worldlines on Orbifolds and the Fayet-Iliopoulos Term
We adapt ``string-inspired'' worldline techniques to one-loop calculations on
orbifolds, in particular on the orbifold. Our method also allows for
the treatment of brane-localized terms, or bulk-brane couplings. For
demonstration, we reproduce the well-known result for the one-loop induced
Fayet-Iliopoulos term in rigidly supersymmetric Abelian gauge theory, and
generalize it to the case where soft supersymmetry breaking mass terms for the
bulk scalar fields are present on the branes.Comment: Typos corrected, clarifying remarks adde
Closing and opening of gap junction pores between two- and threedimensionally cultured tumor cells
Intercellular signal transfer via gap junction pores in cultured multicell spheroids of BICR/M1R-K cells decreases with increasing spheroid age. In two days old spheroids the pores allow passage of Lucifer yellow molecules. Two days later, this fluorescent dye is retained in the injected cell even though the cells are still electrically coupled. Gap junction plaques of considerable size are still found in 9 days old spheroids, when the cells are completely uncoupled. The same cells growing as monolayer cultures do not exhibit such a gradual closing of their gap junction pores: Their coupling is established at first cell contact, probably by a gradual opening of the pores, which remain open even up to 9 days in culture
On SUSY GUTs with a degenerate Higgs mass matrix
Certain supersymmetric grand unified models predict that the coefficients of
the quadratic terms in the MSSM Higgs potential should be degenerate at the GUT
scale. We discuss some examples for such models, and we analyse the
implications of this peculiar condition of a GUT-scale degenerate Higgs mass
matrix for low-scale MSSM phenomenology. To this end we explore the parameter
space which is consistent with existing experimental constraints by means of a
Markov Chain Monte Carlo analysis.Comment: 31 pages, 27 figures; v2: typos correcte
SUSY breaking mediation by throat fields
We investigate, in the general framework of KKLT, the mediation of
supersymmetry breaking by fields propagating in the strongly warped region of
the compactification manifold ('throat fields'). Such fields can couple both to
the supersymmetry breaking sector at the IR end of the throat and to the
visible sector at the UV end. We model the supersymmetry breaking sector by a
chiral superfield which develops an F-term vacuum expectation value. It turns
out that the mediation effect of vector multiplets propagating in the throat
can compete with modulus-anomaly mediation. Moreover, such vector fields are
naturally present as the gauge fields arising from isometries of the throat
(most notably the SO(4) isometry of the Klebanov-Strassler solution). Their
mediation effect is important in spite of their large 4d mass. The latter is
due to the breaking of the throat isometry by the compact manifold at the UV
end of the throat. The contribution from heavy chiral superfields is found to
be subdominant.Comment: 15 pages; v2: typos corrected, references added; v3: comments adde
A million cells in search for contact : multicell spheroids not only for cancer research
Three-dimensional, spherical aggregates of cells - so-called multicell spheroids - have many practical applications. In cancer research, for example, they contribute to a drastic reduction in the number of experiments with animals. The authors of the following article were awarded a special DM 10,000 prize under the Felix-Wankel-Tierschutz-Forschungspreis in November 1986 for their work on intercellular communication in multicell spheroids
Standardisierte in-vitro-Modelle zur Charakterisierung von Stoßwellen
Zum jetzigen Zeitpunkt ist die physikalische Vermessung von Stoßwellen allerdings noch nicht problemlos möglich. Außerdem ist unbekannt, welche Stoßwellenparameter (wie Anstiegszeit und Dauer der Über- und Unterdruckamplitude) für die Steinzertrümmerung und die biologischen Nebenwirkungen bedeutsam sind. Wir haben deshalb vier in vitro-Modelle standardisiert, mit denen sich Wirkungen von Variationen der Behandlungsparameter schnell und zuverlässig aufzeigen lassen. Weiterhin kann die Stoßwellenwirkung auf Zellen, Gewebe und Steine in Lithotriptem mit unterschiedlichen Stoßwellenquellen getestet und verglichen werden
Histopathology of shock wave treated tumor cell suspensions and multicell tumor spheroids
L1210 mouse leukemia cell suspensions exposed to 500 shock waves (SW) in an experimental lithotripter (XLI, Dornier) revealed severe cellular damage. Apart from cell fragments and cellular debris, cells exhibited alterations of shape, vacuolisation of the cytoplasm, perinuclear cisternae, swelling of mitochondria or rupture of the mitochondrial fine structure, and permeabilization of the cell membrane. Treatment of multicell tumor spheroids of both HeLa and EMT6/Ro cells in suspension with 500 SW resulted either in loss of peripheral cells and serious cellular damage in the outer regions or in a fragmentation of the spheroids. Many of the geometrically intact cells exhibited the same histopathological alterations as the suspended L1210 cells. Immobilization of the spheroids in agar or gelatine, however, prevented spheroids from being agitated and accelerated during SW-exposure. After treatment with 500 SW, spheroids immobilized in gelatine were not different from control cultures, as investigated with light- and electronmicroscopy. From our results we conclude that spheroids in suspension are subject to cavitation and liquid jet formation, causing not only acceleration and shearing forces but also collisions which account for the observed cell damage
Cavitation-generated free radicals during shock wave exposure: investigations with cell-free solutions and suspended cells
Extracorporeally generated shock waves as used in lithotripsy of urinary and biliary stones exhibit side effects in vivo. Furthermore, these shock waves destroy eukaryotic cells during in vitro treatment in suspension. A possible cause of these damaging effects might be cavitation, the growth and collapse of bubbles in liquids exposed to tensile stresses. During the collapse, temperature inside these cavitation bubbles rises up to several thousand K, leading to the formation of free radicals. We demonstrated the occurrence of cavitation-generated free radicals by direct reaction with fluorescent dyes in solution after shock wave treatment and investigated the resulting cell killing by variation of the cellular antioxidative defense status. We present evidence for the generation of intracellular free radicals during shock wave treatment of suspended cells
Sensivity of normal and malignant cells to shock waves
We examined the cytotoxic effect of shock waves for primary (embryonic chick kidney and thigh muscle) and permanently growing normal and malignant cells (human, rat, and mouse) in suspension. To avoid the influence of different media, the cells were suspended in phosphate buffered, saline and shock wave treated. In all cases the acute cytotoxic effect (measured by flow cytometry) was a function of the applied shock waves. The investigated cells differed in their LD 50 values which, however, do not reveal a general difference in sensitivity to shock waves for normal and malignant cells
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