700 research outputs found
The Complexity of Combinations of Qualitative Constraint Satisfaction Problems
The CSP of a first-order theory is the problem of deciding for a given
finite set of atomic formulas whether is satisfiable. Let
and be two theories with countably infinite models and disjoint
signatures. Nelson and Oppen presented conditions that imply decidability (or
polynomial-time decidability) of under the
assumption that and are decidable (or
polynomial-time decidable). We show that for a large class of
-categorical theories the Nelson-Oppen conditions are not
only sufficient, but also necessary for polynomial-time tractability of
(unless P=NP)
Unbiased All-Optical Random-Number Generator
The generation of random bits is of enormous importance in modern information
science. Cryptographic security is based on random numbers which require a
physical process for their generation. This is commonly performed by hardware
random number generators. These exhibit often a number of problems, namely
experimental bias, memory in the system, and other technical subtleties, which
reduce the reliability in the entropy estimation. Further, the generated
outcome has to be post-processed to "iron out" such spurious effects. Here, we
present a purely optical randomness generator, based on the bi-stable output of
an optical parametric oscillator. Detector noise plays no role and no further
post-processing is required. Upon entering the bi-stable regime, initially the
resulting output phase depends on vacuum fluctuations. Later, the phase is
rigidly locked and can be well determined versus a pulse train, which is
derived from the pump laser. This delivers an ambiguity-free output, which is
reliably detected and associated with a binary outcome. The resulting random
bit stream resembles a perfect coin toss and passes all relevant randomness
measures. The random nature of the generated binary outcome is furthermore
confirmed by an analysis of resulting conditional entropies.Comment: 10 pages, 4 figure
Inducing vortices in a Bose-Einstein condensate using holographically produced light beams
In this paper we demonstrate a technique that can create out-of-equilibrium
vortex configurations with almost arbitrary charge and geometry in a
Bose-Einstein condensate. We coherently transfer orbital angular momentum from
a holographically generated light beam to a Rubidium 87 condensate using a
two-photon stimulated Raman process. Using matter wave interferometry, we
verify the phase pattern imprinted onto the atomic wave function for a single
vortex and a vortex-antivortex pair. In addition to their phase winding, the
vortices created with this technique have an associated hyperfine spin texture.Comment: 4 pages, 5 figure
Laser textured surfaces for mixed lubrication: Influence of aspect ratio, textured area and dimple arrangement
Unidirectional sliding experiments with polished and laser textured steel surfaces were carried out to investigate the effects of different textured area densities, aspect ratios and dimple arrangements. The system was lubricated with Polyalphaolefin (PAO) at 100 °C and the contact pressure was 3 MPa. For measuring Stribeck curves, the sliding speed was controlled between 40 and 2000 mm/s. The textured area density was varied between 5% and 30%, with the lowest friction values found for 10%. Aspect ratios ranging from 0.02 to 0.2 were investigated and for 0.1 the lowest friction values were measured. The dimple arrangements tested were cubic, hexagonal and a random distribution for a textured area density of 10% and an aspect ratio of 0.1. Our results demonstrate that the dimple arrangement does affect friction values, hinting to the fact that individual texture elements do influence each other. The optimum dimple arrangement was found in a hexagonal packing. This systematic variation of these three key texturing parameters for the morphological texturing of a tribological surface with dimples will allow a strategic choice of texturing parameters. This makes the most of the tremendous potential that laser surface texturing has for reducing friction forces and thereby CO2 emissions
Waviness Affects Friction and Abrasive Wear
Abrasive wear can have a detrimental effect on machinery, especially in the mining and construction industries. To prolong machinery lifetime and cut down energy consumption, a thorough understanding of abrasive wear is essential: surface topography measurement and interpretation (including form, waviness, and roughness) are vitally important. However, the potentially crucial influence of surface topography intricacies on tribological behavior has been obscured since roughness and waviness are considered simple scalar quantities in most cases (e.g., roughness R and waviness W). In this work, the complete waviness profile of the sliding track was used to shed light on the influence of surface topography on abrasive wear. Bearing steel (100Cr6, AISI 52100) pins and disks were tribologically tested in a flat-on-flat contact with AlO-based slurries as interfacial medium. Using slurries with two different particle sizes, 5 and 13 μm, we found that friction fluctuates only with small abrasive particles (5-µm slurry) and relatively low waviness disks. It was found that even small surface deviations (albeit minimized and controlled for) can significantly increase the friction coefficient—up to 91%. Remarkably, not only are frictional fluctuations strongly correlated with the disk’s initial waviness profile, but these small fluctuations correlate with unevenly distributed high wear. These findings enhance our understanding of the friction wear structure and provide the basis for exploring how surfaces can be optimized for better tribological performance
Subunit-Specific Role of NF-κB in Cancer
Kaltschmidt B, Greiner J, Kadhim H, Kaltschmidt C. Subunit-Specific Role of NF-κB in Cancer. Biomedicines. 2018;6(2): 44.The transcription factor NF-kB is a key player in inflammation, cancer development, and
progression. NF-kB stimulates cell proliferation, prevents apoptosis, and could promote tumor
angiogenesis as well as metastasis. Extending the commonly accepted role of NF-kB in cancer
formation and progression, different NF-kB subunits have been shown to be active and of particular
importance in distinct types of cancer. Here, we summarize overexpression data of the NF-kB subunits
RELA, RELB, and c-REL (referring to the v-REL, which is the oncogene of Reticuloendotheliosis
virus strain T) as well as of their upstream kinase inhibitor, namely inhibitor of kB kinases (IKK),
in different human cancers, assessed by database mining. These data argue against a universal
mechanism of cancer-mediated activation of NF-kB, and suggest a much more elaborated mode of
NF-kB regulation, indicating a tumor type-specific upregulation of the NF-kB subunits. We further
discuss recent findings showing the diverse roles of NF-kB signaling in cancer development and
metastasis in a subunit-specific manner, emphasizing their specific transcriptional activity and the
role of autoregulation. While non-canonical NF-kB RELB signaling is described to be mostly present
in hematological cancers, solid cancers reveal constitutive canonical NF-kB RELA or c-REL activity.
Providing a linkage to cancer therapy, we discuss the recently described pivotal role of NF-kB c-REL
in regulating cancer-targeting immune responses. In addition, current strategies and ongoing clinical
trials are summarized, which utilize genome editing or drugs to inhibit the NF-kB subunits for
cancer treatment
Tribological mechanisms of slurry abrasive wear
Abrasive wear mechanisms—including two-body and three-body abrasion—dominate the performance and lifespan of tribological systems in many engineering fields, even of those operating in lubricated conditions. Bearing steel (100Cr6) pins and discs in a flat-on-flat contact were utilized in experiments together with 5 and 13 µm AlO-based slurries as interfacial media to shed light on the acting mechanisms. The results indicate that a speed-induced hydrodynamic effect occurred and significantly altered the systems’ frictional behavior in tests that were performed using the 5 µm slurry. Further experiments revealed that a speed-dependent hydrodynamic effect can lead to a 14% increase in film thickness and a decrease in friction of around 2/3, accompanied by a transition from two-body abrasion to three-body abrasion and a change in wear mechanism from microcutting and microploughing to fatigue wear. Surprisingly, no correlation could be found between the total amount of wear and the operating state of the system during the experiment; however, the wear distribution over pin and disc was observed to change significantly. This paper studies the influence of the hydrodynamic effect on the tribological mechanism of lubricated abrasive wear and also highlights the importance to not only consider a tribological systems’ global amount of wear
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