17 research outputs found
Higher Derivative Quantum Gravity with Gauss-Bonnet Term
Higher derivative theory is one of the important models of quantum gravity,
renormalizable and asymptotically free within the standard perturbative
approach. We consider the renormalization group for this theory,
an approach which proved fruitful in models. A consistent
formulation in dimension requires taking quantum effects of the
topological term into account, hence we perform calculation which is more
general than the ones done before. In the special case we confirm a known
result by Fradkin-Tseytlin and Avramidi-Barvinsky, while contributions from
topological term do cancel. In the more general case of
renormalization group equations there is an extensive ambiguity related to
gauge-fixing dependence. As a result, physical interpretation of these
equations is not universal unlike we treat as a small parameter. In
the sector of essential couplings one can find a number of new fixed points,
some of them have no analogs in the case.Comment: LaTeX file, 30 pages, 5 figures. Several misprints in the
intermediate expressions correcte
Investigation of vibratory drilling model with adaptive control. Part 2: mixed control of peak-to-peak vibration displacement and cutting continuity index
Chip segmentation is important condition for deep drilling efficiency improving. Chip segmentation could be ensured by sustaining stable axial self-excited vibrations of a drill. Vibrations are excited by regenerative effect when cutting edges move along the surface formed by previous passes. The conditions required for reliable chip segmentation could be created by using of a special vibratory head with an elastic element, providing tool additional axial flexibility. To maintain stable vibro-process with amplitude sufficient for chip segmentation, it’s suggested to use the vibratory head with a special actuator for adaptive feedback control proportional to a tool vibration velocity. Two algorithms of the feedback gain adaptation are proposed in the present paper: the adaptation by peak-to-peak displacement and the mixed adaptation by peak-to-peak displacement with cutting continuity index. The investigation of effectiveness of the proposed algorithms applicable to the model, described in [9], is also presented
Chatter suppression in boring with tool position feedback control
Regenerative self-excited vibrations (chatter) often occur in boring operation due to low stiffness of a slender cantilever holder of a tool. These vibrations lead to significant defects of a machined surface and cutting tool damages. The new chatter suppression method is proposed in the paper. Displacement signal measured in the direction which is orthogonal to machined surface is used for generating a control action in the feed direction. Linear proportional control law is applied. Mathematical model of boring process dynamics with control has been developed for validation of the proposed method efficiency and searching better values of feedback gain
Quantum gravity correction, evolution of scalar field and inflation
We take the first nontrivial coefficient of the Schwinger-DeWitt expansion as
a leading correction to the action of the second-derivative metric-dilaton
gravity. To fix the ambiguities related with an arbitrary choice of the gauge
fixing condition and the parametrization for the quantum field, one has to use
the classical equations of motion. As a result, the only corrections are the
ones to the potential of the scalar field. It turns out that the parameters of
the initial classical action may be chosen in such a way that the potential
satisfies most of the conditions for successful inflation.Comment: 11 pages, 3 figure
On the conformal transformation and duality in gravity
The theory described by the sum of the Einstein-Hilbert action and the action
of conformal scalar field possesses the duality symmetry which includes some
special conformal transformation of the metric, and also inversion of scalar
field and of the gravitational constant. In the present paper the conformal
duality is generalized for arbitrary space-time dimension and for
the general sigma-model type conformal scalar theory. We also consider to apply
the conformal duality for the investigation of quantum gravity in the strong
curvature regime. The trace of the first coefficient of the Schwinger-DeWitt
expansion is derived and it's dependence on the gauge fixing condition is
considered. After that we discuss the way to extract the gauge-fixing
independent result and also it's possible physical applications.Comment: LaTeX, 15 pages, no figures. To appear in Classical and Quantum
Gravit
One loop renormalization of the four-dimensional theory for quantum dilaton gravity.
We study the one loop renormalization in the most general metric-dilaton
theory with the second derivative terms only. The general theory can be divided
into two classes, models of one are equivalent to conformally coupled with
gravity scalar field and also to general relativity with cosmological term. The
models of second class have one extra degree of freedom which corresponds to
dilaton. We calculate the one loop divergences for the models of second class
and find that the arbitrary functions of dilaton in the starting action can be
fine-tuned in such a manner that all the higher derivative counterterms
disappear on shell. The only structures in both classical action and
counterterms, which survive on shell, are the potential (cosmological) ones.
They can be removed by renormalization of the dilaton field which acquire the
nontrivial anomalous dimension, that leads to the effective running of the
cosmological constant. For some of the renormalizable solutions of the theory
the observable low energy value of the cosmological constant is small as
compared with the Newtonian constant. We also discuss another application of
our result.Comment: 21 pages, latex, no figures
Effective Action of Vacuum: Semiclassical Approach
We present brief, to great extent pedagogical review on renormalization in
curved space-time and of some recent results on the derivation and better
understanding of quantum corrections to the action of gravity. The paper is
mainly devoted to the semiclassical approach, but we also discuss its
importance for quantum gravity and string theory.Comment: 54 pages, 2 figures, invited review paper partially based on various
lecture courses, accepted in Classical and Quantum Gravity as topical review.
A few changes compared to the original version: some relevant comments on
black hole case and references added, typos correcte
Processing parameters influence on dynamics of vibratory drilling with adaptive control
Chip segmentation is one of necessary conditions of ensuring the deep hole drilling quality when processing hard-to-machine metals. It may be achieved through making drill bit harmonic oscillations in axial direction. Possible way to maintain such vibrations is to replace the standard drilling head with special vibratory head which includes elastic element giving the instrument a possibility to move in axial direction. Self-excitation of drill regenerative oscillations is possible if elastic element stiffness and processing parameters are chosen properly. It is advisable to complement this way of excitation by control action which is determined in feedback circuit and sustains required vibration process characteristics in wide range of processing parameters. In present paper the adaptive control algorithm of vibratory drilling process dynamics is proposed. Control action on oscillation system is proportional to drill vibrational velocity, the feedback gain is determined in adaptation circuit basing on comparison of actual peakto- peak vibrational displacement and its target value. Simulation of closedloop nonlinear system «elastic system – machining process – control system» dynamics has been performed for different values of processing parameters for cases with or without control. The simulation revealed efficiency of suggested algorithm in wide range of processing parameters. Joined influence of processing parameters and target peak-to-peak displacement values on chip breakage conditions is studied. Recommendations for choice of processing parameters and control parameters values are developed. Influence of control action magnitude limit on control system possibilities to achieve control target is analyzed
Suspect Screening and Semi-Quantification of Macrolide Antibiotics in Municipal Wastewater by High-Performance Liquid Chromatography—Precursor Ion Scan Tandem Mass Spectrometry
Macrolides are widely used in medicine and veterinary medicine, and are the leading antibiotics in terms of consumption. The release of macrolides and their metabolites into the environment through municipal wastewater can have an adverse effect on aquatic ecosystems and human health. In the present study, a method for the non-targeted screening and semi-quantitative determination of macrolide antibiotics and their derivatives in wastewater based on a combination of chromatographic separation and tandem mass spectrometric detection in precursor ion scan (PrecIS) mode has been proposed. Product ions with m/z 158 and 174 related to specific desosamine fragments were used as diagnostic ions for the PrecIS detection of the macrolide structures without (14- and 15-membered macrocycles) and with a (16-membered macrocycle) glycosylated desosamine moiety, respectively. The combination of the optimized solid phase extraction procedure and HPLC-MS/MS analysis in PrecIS mode allowed for the suspect screening of macrolides in municipal wastewater with limits of detection in the range of 4–150 ng L−1. The developed approach made it possible to detect and tentatively identify in municipal wastewater 17 compounds belonging to the macrolide class, including azithromycin, clarithromycin, josamycin and 14 metabolites with a total concentration of 1450 ng L−1
Determination of Pentacyclic Triterpenoids in Plant Biomass by Porous Graphitic Carbon Liquid Chromatography—Tandem Mass Spectrometry
Pentacyclic triterpenoids (PCTs), which possess a number of bioactive properties, are considered one of the most important classes of secondary plant metabolites. Their chromatographic determination in plant biomass is complicated by the need to separate a large number of structurally similar compounds belonging to several classes that differ greatly in polarity (monools, diols, and triterpenic acids). This study proposes a rapid, sensitive, and low-cost method for the simultaneous quantification of ten PCTs (3β-taraxerol, lupeol, β-amyrin, α-amyrin, betulin, erythrodiol, uvaol, betulinic, oleanolic, and ursolic acids) by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) using porous graphitic carbon (Hypercarb) as a stationary phase capable of hydrophobic retention and specific interactions with analytes. Revealing the effects of the mobile phase composition, pH, ionic strength, and column temperature on retention and selection of chromatographic conditions on this basis allowed for the effective separation of all target analytes within 8 min in gradient elution mode and attaining limits of detection in the range of 4–104 µg L−1. The developed method was fully validated and successfully tested in the determination of PCTs in common haircap (Polytrichum commune) and prairie sphagnum (Sphagnum palustre) mosses, and fireweed (Chamaenerion angustifolium) stems and leaves