26,728 research outputs found
New nonlinear coherent states and some of their nonclassical properties
We construct a displacement operator type nonlinear coherent state and
examine some of its properties. In particular it is shown that this nonlinear
coherent state exhibits nonclassical properties like squeezing and
sub-Poissonian behaviour.Comment: 3 eps figures. to appear in J.Opt
Cis-regulatory control of the SM50 gene, an early marker of skeletogenic lineage specification in the sea urchin embryo
The SM50 gene encodes a minor matrix protein of the sea urchin embryo spicule. We carried out a detailed functional analysis of a cis-regulatory region of this gene, extending 440 bp upstream and 120 bp downstream of the transcription start site, that had been shown earlier to confer accurate skeletogenic expression of an injected expression vector. The distal portion of this fragment contains elements controlling amplitude of expression, while the region from ā200 to +105 contains spatial control elements that position expression accurately in the skeletogenic lineages of the embryo. A systematic mutagenesis analysis of this region revealed four adjacent regulatory elements, viz two copies of a positively acting sequence (element D) that are positioned just upstream of the transcription start site; an indispensable spatial control element (element C) that is positioned downstream of the start site; and further downstream, a second positively acting sequence (element A). We then constructed a series of synthetic expression constructs. These contained oligonucleotides representing normal and mutated versions of elements D, C, and A, in various combinations. We also changed the promoter of the SM50 gene from a TATA-less to a canonical TATA box form, without any effect on function. Perfect spatial regulation was also produced by a final series of constructs that consisted entirely of heterologous enhancers from the CyIIIa gene, the SV40 early promoter, and synthetic D, C, and A elements. We demonstrate that element C exercises the primary spatial control function of the region we analyzed. We term this a ālocatorā element. This differs from conventional ātissue-specific enhancersā in that while it is essential for expression, it has no transcriptional activity on its own, and it requires other, separable, positive regulatory elements for activity. In the normal configuration these ancillary positive functions are mediated by elements A and D. Only positively acting control elements were observed in the SM50 regulatory domain throughout this analysis
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Introduction: Urban revolutions in the age of global urbanism
This special issue, papers presented at an Urban Studies Foundation-funded conference in Jakarta (March 2011), examines the current āurban centuryā in terms of three revolutions. Revolutions from above index the logics and norms of mainstream global urbanism, particularly the form they have taken as policymakers work with municipal officials worldwide to organise urban development around neoliberal norms. Revolutions from below refer to the multifaceted contestations of global urbanism that take place in and around cities, ranging from urban street demonstrations and occupations (such as those riveting the world in early 2011 when these papers were written) to the quotidian actions of those pursuing politics and livelihoods that subvert the norms of mainstream global urbanism. It also highlights conceptual revolutions, referencing the ongoing challenge of reconceptualising urban theory from the South ā not simply as a hemispheric location or geopolitical category but an epistemological stance, staged from many different locations but always fraught with the differentials of power and the weight of historical geographies. Drawing on the insights of scholars writing from, and not just about, such locations, a further iteration in this āsouthernā turn of urban theorising is proposed. This spatio-temporal conjunctural approach emphasises how the specificity of cities ā their existence as entities that are at once singular and universal ā emerges from spatio-temporal dynamics, connectivities and horizontal and vertical relations. Practically, such scholarship entails taking the field seriously through collaborative work that is multi-sited, engages people along the spectrum of academics and activists, and is presented before and scrutinised by multiple publics
SpZ12-1, a negative regulator required for spatial control of the territory-specific CyIIIa gene in the sea urchin embryo
The CyIIIa cytoskeletal actin gene of the sea urchin Strongylocentrotus purpuratus is activated in late cleavage and expressed exclusively in the aboral ectoderm territory of the embryo. Previous gene transfer studies defined a 2.3 kb cis-regulatory region that is necessary and sufficient for correct temporal and spatial expression of a CyIIIa. CAT fusion gene. In this paper, a negative regulatory element within this region was identified that is required for repression of the CyIIIa gene in skeletogenic mesenchyme cells. The repression mediated by this regulatory element takes place after initial territorial specification. A cDNA clone encoding a DNA-binding protein with twelve Zn fingers (SpZ12-1) was isolated by probing an expression library with this cis-element. Deletion analysis of the SpZ12-1 protein confirmed that a DNA-binding domain is located within the Zn finger region. SpZ12-1 is the only DNA-binding protein in embryo nuclear extract that interacts with the specific cis-target sites required for repression of CyIIIa.CAT in skeletogenic mesenchyme and is likely to be the trans factor that mediates this repression
Physics Prospects at the Hadron Colliders
I start with a brief introduction to the elementary particles and their
interactions, Higgs mechanism and supersymmetry. The major physics objectives
of the Tevatron and LHC colliders are identified. The status and prospects of
the top quark, charged Higgs boson and superparticle searches are discussed in
detail, while those of the neutral Higgs boson(s) are covered in a parallel
talk by R.J.N. Phillips at this workshop.Comment: 16 pages Latex + 15 figures (available on request
Do the precise measurements of the Casimir force agree with the expectations?
An upper limit on the Casimir force is found using the dielectric functions
of perfect crystalline materials which depend only on well defined material
constants. The force measured with the atomic force microscope is larger than
this limit at small separations between bodies and the discrepancy is
significant. The simplest modification of the experiment is proposed allowing
to make its results more reliable and answer the question if the discrepancy
has any relation with the existence of a new force.Comment: 9 pages, LaTeX, 2 Postscript figure
Phase properties of a new nonlinear coherent state
We study phase properties of a displacement operator type nonlinear coherent
state. In particular we evaluate the Pegg-Barnett phase distribution and
compare it with phase distributions associated with the Husimi Q function and
the Wigner function. We also study number- phase squeezing of this state.Comment: 8 eps figures. to appear in J.Opt
The Hamilton-Jacobi Formalism for Higher Order Field Theories
We extend the geometric Hamilton-Jacobi formalism for hamiltonian mechanics
to higher order field theories with regular lagrangian density. We also
investigate the dependence of the formalism on the lagrangian density in the
class of those yelding the same Euler-Lagrange equations.Comment: 25 page
Force Distributions in Frictional Granular Media
We report a joint experimental and theoretical investigation of the
probability distribution functions (pdf's) of the normal and tangential
(frictional) forces in amorphous frictional media. We consider both the joint
pdf of normal and tangential forces together, and the marginal pdf's of normal
forces separately and tangential forces separately. A maximum entropy formalism
is utilized for all these cases after identifying the appropriate constraints.
Excellent agreements with both experimental and simulational data are reported.
The proposed joint pdf (which appears new to the literature) predicts giant
slip events at low pressures, again in agreement with observations.Comment: 13 pages, 15 figure
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