749 research outputs found
Dynamic Characteristics of a Non-symmetric Tilting Pad Journal Bearing
Because tilting-pad journal bearings are more stable and efficient than conventional bearings, they have been commonly applied to many rotating machinery applications. Most of the studies about steady state and dynamic characteristics of tilting-pad journal bearings are usually evaluated by means of thermo hydrodynamic models assuming nominal dimensions for the bearing. However machining errors could lead to actual bearing geometry and dimensions different from the nominal ones. In particular for tilting-pad journal bearing the asymmetry of the bearing geometry is the principal cause of unexpected behavior. In this paper a theoretical analysis on dynamic characteristics of a five-pad tilting-pad journal bearing is investigated with non-nominal geometry, that is, different thickness for each pad. The dynamic coefficients of a five-pad tilting-pad journal bearing with a nominal diameter of 100 mm, length-to-diameter ratio (L/D) of 0.7 are evaluated versus rotor rotational speed, load direction and static load. Then, the analytical results of the non-nominal bearing are compared to those of a bearing having nominal (i.e. ideal) geometry
The Minimal Solution to the mu/B_mu Problem in Gauge Mediation
We provide a minimal solution to the mu/B_mu problem in the gauge mediated
supersymmetry breaking by introducing a Standard Model singlet filed S with a
mass around the messenger scale which couples to the Higgs and messenger
fields. This singlet is nearly supersymmetric and acquires a relatively small
Vacuum Expectation Value (VEV) from its radiatively generated tadpole term.
Consequently, both mu and B_mu parameters receive the tree-level and one-loop
contributions, which are comparable due to the small S VEV. Because there
exists a proper cancellation in such two kinds of contributions to B_mu, we can
have a viable Higgs sector for electroweak symmetry breaking.Comment: 15 pages, 2 figures, version published on JHE
Solving the mu problem with a heavy Higgs boson
We discuss the generation of the mu-term in a class of supersymmetric models
characterized by a low energy effective superpotential containing a term lambda
S H_1 H_2 with a large coupling lambda~2. These models generically predict a
lightest Higgs boson well above the LEP limit of 114 GeV and have been shown to
be compatible with the unification of gauge couplings. Here we discuss a
specific example where the superpotential has no dimensionful parameters and we
point out the relation between the generated mu-term and the mass of the
lightest Higgs boson. We discuss the fine-tuning of the model and we find that
the generation of a phenomenologically viable mu-term fits very well with a
heavy lightest Higgs boson and a low degree of fine-tuning. We discuss
experimental constraints from collider direct searches, precision data, thermal
relic dark matter abundance, and WIMP searches finding that the most natural
region of the parameter space is still allowed by current experiments. We
analyse bounds on the masses of the superpartners coming from Naturalness
arguments and discuss the main signatures of the model for the LHC and future
WIMP searches.Comment: Extended discussion of the LHC phenomenology, as published on JHEP
plus an addendum on the existence of further extremal points of the
potential. 47 pages, 16 figure
Comprehensive molecular characterisation of epilepsy-associated glioneuronal tumours
Glioneuronal tumours are an important cause of treatment-resistant epilepsy. Subtypes of tumour are often poorly discriminated by histological features and may be difficult to diagnose due to a lack of robust diagnostic tools. This is illustrated by marked variability in the reported frequencies across different epilepsy surgical series. To address this, we used DNA methylation arrays and RNA sequencing to assay the methylation and expression profiles within a large cohort of glioneuronal tumours. By adopting a class discovery approach, we were able to identify two distinct groups of glioneuronal tumour, which only partially corresponded to the existing histological classification. Furthermore, by additional molecular analyses, we were able to identify pathogenic mutations in BRAF and FGFR1, specific to each group, in a high proportion of cases. Finally, by interrogating our expression data, we were able to show that each molecular group possessed expression phenotypes suggesting different cellular differentiation: astrocytic in one group and oligodendroglial in the second. Informed by this, we were able to identify CCND1, CSPG4, and PDGFRA as immunohistochemical targets which could distinguish between molecular groups. Our data suggest that the current histological classification of glioneuronal tumours does not adequately represent their underlying biology. Instead, we show that there are two molecular groups within glioneuronal tumours. The first of these displays astrocytic differentiation and is driven by BRAF mutations, while the second displays oligodendroglial differentiation and is driven by FGFR1 mutations
A Complete Model of Low-Scale Gauge Mediation
Recent signs of a Standard Model-like Higgs at 125 GeV point towards large
A-terms in the MSSM. This presents special challenges for gauge mediation,
which by itself predicts vanishing A-terms at the messenger scale. In this
paper, we review the general problems that arise when extending gauge mediation
to achieve large A-terms, and the mechanisms that exist to overcome them. Using
these mechanisms, we construct weakly-coupled models of low-scale gauge
mediation with extended Higgs-messenger couplings that generate large A-terms
at the messenger scale and viable mu/B_mu-terms. Our models are simple,
economical, and complete realizations of supersymmetry at the weak scale.Comment: 33 pages; v2: refs added, minor change
Single-Scale Natural SUSY
We consider the prospects for natural SUSY models consistent with current
data. Recent constraints make the standard paradigm unnatural so we consider
what could be a minimal extension consistent with what we now know. The most
promising such scenarios extend the MSSM with new tree-level Higgs interactions
that can lift its mass to at least 125 GeV and also allow for flavor-dependent
soft terms so that the third generation squarks are lighter than current bounds
on the first and second generation squarks. We argue that a common feature of
almost all such models is the need for a new scale near 10 TeV, such as a scale
of Higgsing or confinement of a new gauge group. We consider the question
whether such a model can naturally derive from a single mass scale associated
with supersymmetry breaking. Most such models simply postulate new scales,
leaving their proximity to the scale of MSSM soft terms a mystery. This
coincidence problem may be thought of as a mild tuning, analogous to the usual
mu problem. We find that a single mass scale origin is challenging, but suggest
that a more natural origin for such a new dynamical scale is the gravitino
mass, m_{3/2}, in theories where the MSSM soft terms are a loop factor below
m_{3/2}. As an example, we build a variant of the NMSSM where the singlet S is
composite, and the strong dynamics leading to compositeness is triggered by
masses of order m_{3/2} for some fields. Our focus is the Higgs sector, but our
model is compatible with a light stop (with the other generation squarks heavy,
or with R-parity violation or another mechanism to hide them from current
searches). All the interesting low-energy mass scales, including linear terms
for S playing a key role in EWSB, arise dynamically from the single scale
m_{3/2}. However, numerical coefficients from RG effects and wavefunction
factors in an extra dimension complicate the otherwise simple story.Comment: 32 pages, 3 figures; version accepted by JHE
(De)Constructing a Natural and Flavorful Supersymmetric Standard Model
Using the framework of deconstruction, we construct simple, weakly-coupled
supersymmetric models that explain the Standard Model flavor hierarchy and
produce a flavorful soft spectrum compatible with precision limits. Electroweak
symmetry breaking is fully natural; the mu-term is dynamically generated with
no B mu-problem and the Higgs mass is easily raised above LEP limits without
reliance on large radiative corrections. These models possess the distinctive
spectrum of superpartners characteristic of "effective supersymmetry": the
third generation superpartners tend to be light, while the rest of the scalars
are heavy.Comment: 36 pages, 4 figures ; v2: references added, expanded discussion of
FCNC
Reverse Engineering Time Discrete Finite Dynamical Systems: A Feasible Undertaking?
With the advent of high-throughput profiling methods, interest in reverse engineering the structure and dynamics of biochemical networks is high. Recently an algorithm for reverse engineering of biochemical networks was developed by Laubenbacher and Stigler. It is a top-down approach using time discrete dynamical systems. One of its key steps includes the choice of a term order, a technicality imposed by the use of Gröbner-bases calculations. The aim of this paper is to identify minimal requirements on data sets to be used with this algorithm and to characterize optimal data sets. We found minimal requirements on a data set based on how many terms the functions to be reverse engineered display. Furthermore, we identified optimal data sets, which we characterized using a geometric property called âgeneral positionâ. Moreover, we developed a constructive method to generate optimal data sets, provided a codimensional condition is fulfilled. In addition, we present a generalization of their algorithm that does not depend on the choice of a term order. For this method we derived a formula for the probability of finding the correct model, provided the data set used is optimal. We analyzed the asymptotic behavior of the probability formula for a growing number of variables n (i.e. interacting chemicals). Unfortunately, this formula converges to zero as fast as , where and . Therefore, even if an optimal data set is used and the restrictions in using term orders are overcome, the reverse engineering problem remains unfeasible, unless prodigious amounts of data are available. Such large data sets are experimentally impossible to generate with today's technologies
An opportunistic cognitive radio communication through the exploitation of the small-scale fading mechanisms of the LTE mobile channel
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