3,675 research outputs found
Subvarieties of generic hypersurfaces in any variety
Let W be a projective variety of dimension n+1, L a free line bundle on W, X
in a hypersurface of degree d which is generic among those given by
sums of monomials from , and let be a generically finite map
from a smooth m-fold Y. We suppose that f is r-filling, i.e. upon deforming X
in , f deforms in a family such that the corresponding deformations
of dominate . Under these hypotheses we give a lower bound for the
dimension of a certain linear system on the Cartesian product having
certain vanishing order on a diagonal locus as well as on a double point locus.
This yields as one application a lower bound on the dimension of the linear
system |K_{Y} - (d - n + m)f^*L - f^*K_{W}| which generalizes results of Ein
and Xu (and in weaker form, Voisin). As another perhaps more surprising
application, we conclude a lower bound on the number of quadrics containing
certain projective images of Y.Comment: We made some improvements in the introduction and definitions. In an
effort to clarify the arguments we separated the 1-filling case from the
r-filling case and we gave a more detailed proof of the key lemma. The
article will appear in the Math. Proc. Cambridge Philos. So
Trisecant Lemma for Non Equidimensional Varieties
The classic trisecant lemma states that if is an integral curve of
\PP^3 then the variety of trisecants has dimension one, unless the curve is
planar and has degree at least 3, in which case the variety of trisecants has
dimension 2. In this paper, our purpose is first to present another derivation
of this result and then to introduce a generalization to non-equidimensional
varities. For the sake of clarity, we shall reformulate our first problem as
follows. Let be an equidimensional variety (maybe singular and/or
reducible) of dimension , other than a linear space, embedded into \PP^r,
. The variety of trisecant lines of , say , has
dimension strictly less than , unless is included in a
dimensional linear space and has degree at least 3, in which case
. Then we inquire the more general case, where is
not required to be equidimensional. In that case, let be a possibly
singular variety of dimension , that may be neither irreducible nor
equidimensional, embedded into \PP^r, where , and a proper
subvariety of dimension . Consider now being a component of
maximal dimension of the closure of \{l \in \G(1,r) \vtl \exists p \in Y, q_1,
q_2 \in Z \backslash Y, q_1,q_2,p \in l\}. We show that has dimension
strictly less than , unless the union of lines in has dimension ,
in which case . In the latter case, if the dimension of the space
is stricly greater then , the union of lines in cannot cover the whole
space. This is the main result of our work. We also introduce some examples
showing than our bound is strict
Erosion-induced massive organic carbon burial and carbon emission in the Yellow River basin, China
Soil erosion and terrestrial deposition of soil organic carbon (SOC) can
potentially play a significant role in global carbon cycling. Assessing the
redistribution of SOC during erosion and subsequent transport and burial is
of critical importance. Using hydrological records of soil erosion and
sediment load, and compiled organic carbon (OC) data, estimates of the eroded
soils and OC induced by water in the Yellow River basin during the period
1950–2010 were assembled. The Yellow River basin has experienced intense
soil erosion due to combined impact of natural process and human activity.
Over the period, 134.2 ± 24.7 Gt of soils and 1.07 ± 0.15 Gt of
OC have been eroded from hillslopes based on a soil erosion rate of
1.7–2.5 Gt yr<sup>−1</sup>. Approximately 63% of the eroded soils were
deposited in the river system, while only 37% were discharged into the
ocean. For the OC budget, approximately 0.53 ± 0.21 Gt (49.5%) was
buried in the river system, 0.25 ± 0.14 Gt (23.5%) was delivered
into the ocean, and the remaining 0.289 ± 0.294 Gt (27%) was
decomposed during the erosion and transport processes. This validates the
commonly held assumption that 20–40% of the eroded OC would be oxidized
after erosion. Erosion-induced OC redistribution on the landscape likely
represented a carbon source, although a large proportion of OC was buried. In
addition, about half of the terrestrially redeposited OC (49.4%) was
buried behind dams, revealing the importance of dam trapping in sequestering
the eroded OC. Although several uncertainties need to be better constrained,
the obtained budgetary results provide a means of assessing the
redistribution of the eroded OC within the Yellow River basin. Human
activities have significantly altered its redistribution pattern over the
past decades
Influence of Fermion Velocity Renormalization on Dynamical Mass Generation in QED
We study dynamical fermion mass generation in (2+1)-dimensional quantum
electrodynamics with a gauge field coupling to massless Dirac fermions and
non-relativistic scalar bosons. We calculate the fermion velocity
renormalization and then examine its influence on dynamical mass generation by
using the Dyson-Schwinger equation. It is found that dynamical mass generation
takes place even after including the scalar bosons as long as the bosonic
compressibility parameter is sufficiently small. In addition, the fermion
velocity renormalization enhances the dynamically generated mass.Comment: 6 pages, 3 figures, Chinese Physics Letter, Vol 29, page 057401(2012
Combined regenerated fibre Bragg gratings and Fabry-Perot etalons for dual strain and temperature sensing
© 2015 SPIE. A highly integrated fibre-optic sensor with regenerated fibre Bragg grating (RFBG) and a micro Fabry-Pérot (MFP) is proposed and demonstrated for simultaneous measurement of temperature and strain under high temperature (> 600°C). The MFP is fabricated by using a 157 nm fluorine gas (F2) laser to micromachine the core of a standard optical fibre. The RFBG is fabricated by regenerating a seed grating written over the Fabry-Pérot. Since the MFP and RFBG have different sensitivity coefficients, their combination can be used to realise simultaneous measurement of temperature and strain. It is believed that such a high-temperature strain sensor could find important applications in many areas where simultaneous measurement of temperature and strain under high temperature is required
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