1,417 research outputs found
A handbook of Nebraska grasses : with illustrated keys for their identification, together with a general account of their structure and economic importance
The true grasses belong to the one family Poaceae, often called Gramineae, and constitute a very well defined natural group of plants. This family comprises upward of 3,000 species distributed among almost 300 genera. From the economic point of view the family is of supreme importance thru the fact that here belong the cereals, which supply a large part of the food of man, and the forage grasses which are so important as feed for our domesticated animals. The genera and species are for the most part separated by artificial charactersâa fact which renders their study and identification extremely difficult even for the expert. The experience of the authors has convinced them that much of this difficulty is to be credited to the keys found in our common manuals. Theoretically a key is intended to assist one in properly identifying a plant, but actually many of the keys, upon close inspection. are found to contain so many vague and contradictory statements that they can be depended upon only by the expert who, on account of his working knowledge, makes slight use of the keys. It occurred to the senior author some years ago that an illustrated key might solve many of these difficulties. An accurate illustration conveys a more definite idea of any particular structure and leaves less room for doubt than any number of words. In fact, the serious and annoying inaccuracies of most keys to the grasses became more and more apparent as the work of preparing the illustrations progressed. The authors are fully convinced that illustrated keys of the type here employed will prove useful in many other groups of plants. The nomenclature here employed is largely that of the seventh edition of Gray\u27s Manualâtho our purpose has not been to insist upon any particular name but to provide means whereby the student can with some certainty attach to any given plant some one name which has been properly authorized. The present key includes most of the species known to occur in Nebraska, tho a few of minor importance and very restricted distribution have been omitted. There are provided also some data on the economic value of certain of the most important species. The illustrations for the grass keys have been drawn expressly for this publication. They are derived in part from actual authentic specimens and in part redrawn in modified form from various manuals and monographs. T he authors have made free use of the manuals, monographs. etc., included in the Bibliography and take this opportunity to commend these publications to the attention of all who wish to learn more of our common grasses. It is hoped that the keys here presented will facilitate the study of the grass flora of Nebraska by farmers and students
Abelian symmetries in multi-Higgs-doublet models
N-Higgs doublet models (NHDM) are a popular framework to construct
electroweak symmetry breaking mechanisms beyond the Standard model. Usually,
one builds an NHDM scalar sector which is invariant under a certain symmetry
group. Although several such groups have been used, no general analysis of
symmetries possible in the NHDM scalar sector exists. Here, we make the first
step towards this goal by classifying the elementary building blocks, namely
the abelian symmetry groups, with a special emphasis on finite groups. We
describe a strategy that identifies all abelian groups which are realizable as
symmetry groups of the NHDM Higgs potential. We consider both the groups of
Higgs-family transformations only and the groups which also contain generalized
CP transformations. We illustrate this strategy with the examples of 3HDM and
4HDM and prove several statements for arbitrary N.Comment: 33 pages, 2 figures; v2: conjecture 3 is proved and becomes theorem
3, more explanations of the main strategy are added, matches the published
versio
Anisotropic susceptibility of ferromagnetic ultrathin Co films on vicinal Cu
We measure the magnetic susceptibility of ultrathin Co films with an in-plane
uniaxial magnetic anisotropy grown on a vicinal Cu substrate. Above the Curie
temperature the influence of the magnetic anisotropy can be investigated by
means of the parallel and transverse susceptibilities along the easy and hard
axes. By comparison with a theoretical analysis of the susceptibilities we
determine the isotropic exchange interaction and the magnetic anisotropy. These
calculations are performed in the framework of a Heisenberg model by means of a
many-body Green's function method, since collective magnetic excitations are
very important in two-dimensional magnets.Comment: 7 pages, 3 figure
Model-Independent Semileptonic Form Factors Using Dispersion Relations
We present a method for parametrizing heavy meson semileptonic form factors
using dispersion relations, and from it produce a two-parameter description of
the B -> B elastic form factor. We use heavy quark symmetry to relate this
function to B -> D* l nu form factors, and extract
|V_cb|=0.0355^{+0.0029}_{-0.0025} from experimental data with a least squares
fit. Our method eliminates model-dependent uncertainties inherent in choosing a
parametrization for the extrapolation of the differential decay rate to
threshold.Comment: uses lanlmac(harvmac) and epsf, 12 pages, 1 eps figure included (Talk
by BG at the 6-th International Symposium on Heavy Flavour Physics, Pisa,
Italy, 6--10 June, 1995
Spontaneous time reversal symmetry breaking in the pseudogap state of high-Tc superconductors
When matter undergoes a phase transition from one state to another, usually a
change in symmetry is observed, as some of the symmetries exhibited are said to
be spontaneously broken. The superconducting phase transition in the underdoped
high-Tc superconductors is rather unusual, in that it is not a mean-field
transition as other superconducting transitions are. Instead, it is observed
that a pseudo-gap in the electronic excitation spectrum appears at temperatures
T* higher than Tc, while phase coherence, and superconductivity, are
established at Tc (Refs. 1, 2). One would then wish to understand if T* is just
a crossover, controlled by fluctuations in order which will set in at the lower
Tc (Refs. 3, 4), or whether some symmetry is spontaneously broken at T* (Refs.
5-10). Here, using angle-resolved photoemission with circularly polarized
light, we find that, in the pseudogap state, left-circularly polarized photons
give a different photocurrent than right-circularly polarized photons, and
therefore the state below T* is rather unusual, in that it breaks time reversal
symmetry11. This observation of a phase transition at T* provides the answer to
a major mystery of the phase diagram of the cuprates. The appearance of the
anomalies below T* must be related to the order parameter that sets in at this
characteristic temperature .Comment: 11 pages, 4 figure
The heavy top quark in the two Higgs doublet model
Constraints on the two Higgs doublet model are presented, assuming a top mass
of 174 17 GeV. We concentrate primarily on the ``type II'' model, where
up--type quarks receive their mass from one Higgs doublet, and down--type
quarks receive their mass from the second doublet. High energy constraints
derived from the mass, the full width of the and the partial
width of the are combined with low energy constraints from , and - mixing to
determine the experimentally favored configurations of the model. This
combination of observables rules out small charged Higgs masses and small
values of , and provides some information about the neutral Higgs
masses and the mixing angle . In particular, constraints derived from
the parameter rule out configurations where the charged Higgs is much
heavier or much lighter than the neutral Higgses. We discuss a scenario where
is enhanced relative to the standard model result,
which unfortunately is on the verge of being ruled out by the combination of
and parameter constraints. Implications for
various extensions of the standard model are briefly discussed.Comment: 26 page
Nuclear Attenuation of Fast Hadrons Produced in Charged-Current Neutrino and Antineutrino Interactions in Neon
The production of hadrons in charged-current (anti)neutrino interactions is
studied with the bubble chamber BEBC exposed ot the CERN (anti)neutrino
wide-band beam. Fast-hadron production in a neon target is found to be
attennuated as compared to that in a hydrogen target. This feature is discussed
within the theoretical models based on the idea of a hadron formation length.
The experimental results favour the `constituent' over the `yo-yo' length
concept, and suggest a quark cross-section in the order of 3mb.Comment: 14 pages + 7 figures, ps fil
The mechanisms of Yu Ping Feng San in tracking the cisplatin-resistance by regulating ATP-binding cassette transporter and glutathione S-transferase in lung cancer cells
Cisplatin is one of the first line anti-cancer drugs prescribed for treatment of solid tumors; however, the chemotherapeutic drug resistance is still a major obstacle of cisplatin in treating cancers. Yu Ping Feng San (YPFS), a well-known ancient Chinese herbal combination formula consisting of Astragali Radix, Atractylodis Macrocephalae Rhizoma and Saposhnikoviae Radix, is prescribed as a herbal decoction to treat immune disorders in clinic. To understand the fast-onset action of YPFS as an anti-cancer drug to fight against the drug resistance of cisplatin, we provided detailed analyses of intracellular cisplatin accumulation, cell viability, and expressions and activities of ATP-binding cassette transporters and glutathione S-transferases (GSTs) in YPFS-treated lung cancer cell lines. In cultured A549 or its cisplatin-resistance A549/DDP cells, application of YPFS increased accumulation of intracellular cisplatin, resulting in lower cell viability. In parallel, the activities and expressions of ATP-binding cassette transporters and GSTs were down-regulated in the presence of YPFS. The expression of p65 subunit of NF-ÎșB complex was reduced by treating the cultures with YPFS, leading to a high ratio of Bax/Bcl-2, i.e. increasing the rate of cell death. Prim-O-glucosylcimifugin, one of the abundant ingredients in YPFS, modulated the activity of GSTs, and then elevated cisplatin accumulation, resulting in increased cell apoptosis. The present result supports the notion of YPFS in reversing drug resistance of cisplatin in lung cancer cells by elevating of intracellular cisplatin, and the underlying mechanism may be down regulating the activities and expressions of ATP-binding cassette transporters and GSTs
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