3,073 research outputs found
Projectivity of Planar Zeros in Field and String Theory Amplitudes
We study the projective properties of planar zeros of tree-level scattering
amplitudes in various theories. Whereas for pure scalar field theories we find
that the planar zeros of the five-point amplitude do not enjoy projective
invariance, coupling scalars to gauge fields gives rise to tree-level
amplitudes whose planar zeros are determined by homogeneous polynomials in the
stereographic coordinates labelling the direction of flight of the outgoing
particles. In the case of pure gauge theories, this projective structure is
generically destroyed if string corrections are taken into account. Scattering
amplitudes of two scalars with graviton emission vanish exactly in the planar
limit, whereas planar graviton amplitudes are zero for helicity violating
configurations. These results are corrected by string effects, computed using
the single-valued projection, which render the planar amplitude nonzero.
Finally, we discuss how the structure of planar zeros can be derived from the
soft limit behavior of the scattering amplitudes.Comment: 39 page, 5 figures. v2: typos corrected. It matches the version
published in Journal of High Energy Physic
Semiclassical (Quantum Field Theory) and Quantum (String) de Sitter Regimes: New Results
We compute the quantum string entropy S_s(m, H) from the microscopic string
density of states rho_s (m,H) of mass m in de Sitter space-time. We find for
high m, a {\bf new} phase transition at the critical string temperature T_s=
(1/2 pi k_B)L c^2/alpha', higher than the flat space (Hagedorn) temperature
t_s. (L = c/H, the Hubble constant H acts at the transition as producing a
smaller string constant alpha' and thus, a higher tension). T_s is the precise
quantum dual of the semiclassical (QFT Hawking-Gibbons) de Sitter temperature
T_sem = hbar c /(2\pi k_B L). We find a new formula for the full de Sitter
entropy S_sem (H), as a function of the usual Bekenstein-Hawking entropy
S_sem^(0)(H). For L << l_{Planck}, ie. for low H << c/l_Planck,
S_{sem}^{(0)}(H) is the leading term, but for high H near c/l_Planck, a new
phase transition operates and the whole entropy S_sem (H) is drastically
different from the Bekenstein-Hawking entropy S_sem^(0)(H). We compute the
string quantum emission cross section by a black hole in de Sitter (or
asymptotically de Sitter) space-time (bhdS). For T_sem ~ bhdS << T_s, (early
evaporation stage), it shows the QFT Hawking emission with temperature T_sem ~
bhdS, (semiclassical regime). For T_sem ~ bhdS near T_{s}, it exhibits a phase
transition into a string de Sitter state of size L_s = l_s^2/L}, l_s=
\sqrt{\hbar alpha'/c), and string de Sitter temperature T_s. Instead of
featuring a single pole singularity in the temperature (Carlitz transition), it
features a square root branch point (de Vega-Sanchez transition). New bounds on
the black hole radius r_g emerge in the bhdS string regime: it can become r_g =
L_s/2, or it can reach a more quantum value, r_g = 0.365 l_s.Comment: New original materia
Economical comparison of CHP systems for industrial user with large steam demand
In this paper cogeneration benefits applied to a user with a high steam demand are analyzed. The methodology for the feasibility study and the economical analysis of the investment is presented under the Italian legislative framework. The methodology is applied to an actual case and a detailed description and discussion of all data input is provided. Especially this last key point will be faced using starting data usually available in these kind of studies (i.e., not very detailed for thermal consumption). Finally a comparison of different CHP technologies and a sensitivity analysis is done
Semiclassical (QFT) and Quantum (String) anti - de Sitter Regimes: New Results
We compute the quantum string entropy S_s(m, H) from the microscopic string
density of states of mass m in Anti de Sitter space-time. For high m, (high Hm
-->c/\alpha'), no phase transition occurs at the Anti de Sitter string
temperature T_{s} which is higher than the flat space (Hagedorn) temperature
t_{s}. (the Hubble constant H acts as producing a smaller string constant and
thus, a higher tension). T_s is the precise quantum dual of the semiclassical
(QFT) Anti de Sitter temperature scale . We compute the quantum string emission
by a black hole in Anti de Sitter space-time (bhAdS). In the early evaporation
stage, it shows the QFT Hawking emission with temperature T_{sem~bhAdS},
(semiclassical regime). For T_{sem~bhAdS}--> T_{s}, it exhibits a phase
transition into a Anti de Sitter string state. New string bounds on the black
hole emerge in the bhAdS string regime. We find a new formula for the full
(quantum regime included) Anti de Sitter entropy S_{sem}, as a function of the
usual Bekenstein-Hawking entropy S_{sem}^(0). For low H (semiclassical regime),
S_{sem}^(0) is the leading term but for high H (quantum regime), no phase
transition operates, in contrast to de Sitter space, and the entropy S_{sem} is
very different from the Bekenstein-Hawking term S_{sem}^(0).Comment: Comments 26 pages; no figure
Semiclassical (QFT) and Quantum (String) Rotating Black Holes and their Evaporation: New Results
Combination of both quantum field theory (QFT) and string theory in curved
backgrounds in a consistent framework, the string analogue model, allows us to
provide a full picture of the Kerr-Newman black hole and its evaporation going
beyond the current picture. We compute the quantum emission cross section of
strings by a Kerr-Newmann black hole (KNbh). It shows the black hole emission
at the Hawking temperature T_{sem} in the early evaporation and the new string
emission featuring a Hagedorn transition into a string state of temperature T_
s at the last stages. New bounds on the angular momentum J and charge Q emerge
in the quantum string regime. The last state of evaporation of a semiclassical
KNbh is a string state of temperature T_s, mass M_s, J = 0 = Q, decaying as a
quantum string into all kinds of particles.(There is naturally, no loss of
information, (no paradox at all)). We compute the microscopic string entropy
S_s(m, j) of mass m and spin mode j. (Besides the usual transition at T_s), we
find for high j, (extremal string states) a new phase transition at a
temperature T_{sj} higher than T_s. We find a new formula for the Kerr black
hole entropy S_{sem}, as a function of the usual Bekenstein-Hawking entropy .
For high angular momentum, (extremal J = GM^2/c), a gravitational phase
transition operates and the whole entropy S_{sem} is drastically different from
the Bekenstein-Hawking entropy. This new extremal black hole transition occurs
at a temperature T_{sem J} higher than the Hawking temperature T_{sem}.Comment: New articl
Fluid-Fluid Reactions: Study of the Surface Renewal Theory in Chemical Engineering Courses
The Surface Renewal Theory (SRT) is one of the most unfamiliar models in order to characterize fluid-fluid and fluid-fluid-solid reactions, which are of considerable industrial and academicals importance. In the present work, an approach to the resolution of the SRT model by numerical methods is presented, enabling the visualization of the influence of different variables which control the heterogeneous overall process. Its use in a classroom allowed the students to reach a great understanding of the process
Robot Impedance Control and Passivity Analysis with Inner Torque and Velocity Feedback Loops
Impedance control is a well-established technique to control interaction
forces in robotics. However, real implementations of impedance control with an
inner loop may suffer from several limitations. Although common practice in
designing nested control systems is to maximize the bandwidth of the inner loop
to improve tracking performance, it may not be the most suitable approach when
a certain range of impedance parameters has to be rendered. In particular, it
turns out that the viable range of stable stiffness and damping values can be
strongly affected by the bandwidth of the inner control loops (e.g. a torque
loop) as well as by the filtering and sampling frequency. This paper provides
an extensive analysis on how these aspects influence the stability region of
impedance parameters as well as the passivity of the system. This will be
supported by both simulations and experimental data. Moreover, a methodology
for designing joint impedance controllers based on an inner torque loop and a
positive velocity feedback loop will be presented. The goal of the velocity
feedback is to increase (given the constraints to preserve stability) the
bandwidth of the torque loop without the need of a complex controller.Comment: 14 pages in Control Theory and Technology (2016
Comparison of gene coverage of mouse oligonucleotide microarray platforms
BACKGROUND: The increasing use of DNA microarrays for genetical genomics studies generates a need for platforms with complete coverage of the genome. We have compared the effective gene coverage in the mouse genome of different commercial and noncommercial oligonucleotide microarray platforms by performing an in-house gene annotation of probes. We only used information about probes that is available from vendors and followed a process that any researcher may take to find the gene targeted by a given probe. In order to make consistent comparisons between platforms, probes in each microarray were annotated with an Entrez Gene id and the chromosomal position for each gene was obtained from the UCSC Genome Browser Database. Gene coverage was estimated as the percentage of Entrez Genes with a unique position in the UCSC Genome database that is tested by a given microarray platform. RESULTS: A MySQL relational database was created to store the mapping information for 25,416 mouse genes and for the probes in five microarray platforms (gene coverage level in parenthesis): Affymetrix430 2.0 (75.6%), ABI Genome Survey (81.24%), Agilent (79.33%), Codelink (78.09%), Sentrix (90.47%); and four array-ready oligosets: Sigma (47.95%), Operon v.3 (69.89%), Operon v.4 (84.03%), and MEEBO (84.03%). The differences in coverage between platforms were highly conserved across chromosomes. Differences in the number of redundant and unspecific probes were also found among arrays. The database can be queried to compare specific genomic regions using a web interface. The software used to create, update and query the database is freely available as a toolbox named ArrayGene. CONCLUSION: The software developed here allows researchers to create updated custom databases by using public or proprietary information on genes for any organisms. ArrayGene allows easy comparisons of gene coverage between microarray platforms for any region of the genome. The comparison presented here reveals that the commercial microarray Sentrix, which is based on the MEEBO public oligoset, showed the best mouse genome coverage currently available. We also suggest the creation of guidelines to standardize the minimum set of information that vendors should provide to allow researchers to accurately evaluate the advantages and disadvantages of using a given platform
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