arXiv subjects

Menas Kafatos

Publications and source records attributed to Menas Kafatos.

17 recordsLinked to original sources

arXiv2020

Patterns of population displacement during mega-fires in California detected using Facebook Disaster Maps

Facebook Disaster Maps (FBDM) is the first platform providing analysis-ready population change products derived from crowdsourced data targeting disaster relief practices. We evaluate the representativeness of FBDM data using the Mann-Kendall test and emerging hot and cold spots in an anomaly analysis to reveal the trend, magnitude, and agglommeration of population displacement during the Mendocino Complex and Woolsey fires in California, USA. Our results show that the distribution of FBDM pre-crisis users fits well with the total population from different sources. Due to usage habits, the elder population is underrepresented in FBDM data. During the two mega-fires in California, FBDM data effectively captured the temporal change of population arising from the placing and lifting of evacuation orders. Coupled with monotonic trends, the fall and rise of cold and hot spots of population revealed the areas with the greatest population drop and potential places to house the displaced residents. A comparison between the Mendocino Complex and Woolsey fires indicates that a densely populated region can be evacuated faster than a scarcely populated one, possibly due to the better access to transportation. In sparsely populated fire-prone areas, resources should be prioritized to move people to shelters as the displaced residents do not have many alternative options, while their counterparts in densely populated areas can utilize their social connections to seek temporary stay at nearby locations during an evacuation. Integrated with an assessment on underrepresented communities, FBDM data and the derivatives can provide much needed information of near real-time population displacement for crisis response and disaster relief. As applications and data generation mature, FBDM will harness crowdsourced data and aid first responder decision-making.

cs.CY↗

arXiv2014

Veiled Nonlocality and Cosmic Censorship

The premise that consciousness has a quantum mechanical basis or correlate implies that its workings have a nonlocal component. To check whether consciousness as an entity leaves a physical trace, we propose that laboratory searches for such a trace should be for nonlocality, where probabilities do not conform to local expectations. Starting with the idea that nonlocality may be veiled as one of the ways cosmic censorship operates, we further argue that in order to preserve the ordinary objective reality described by local realism and general relativity, veiled nonlocality and cosmic censorship are indispensable operational aspects of the interactions of observers with physical systems. Nevertheless, it may be possible to indirectly detect traces of nonlocality in experiments where humans and other sentient subjects are involved

quant-ph↗

arXiv2011

Atmosphere-Ionosphere Response to the M9 Tohoku Earthquake Revealed by Joined Satellite and Ground Observations. Preliminary results

The recent M9 Tohoku Japan earthquake of March 11, 2011 was the largest recorded earthquake ever to hit this nation. We retrospectively analyzed the temporal and spatial variations of four different physical parameters - outgoing long wave radiation (OLR), GPS/TEC, Low-Earth orbit tomography and critical frequency foF2. These changes characterize the state of the atmosphere and ionosphere several days before the onset of this earthquake. Our first results show that on March 8th a rapid increase of emitted infrared radiation was observed from the satellite data and an anomaly developed near the epicenter. The GPS/TEC data indicate an increase and variation in electron density reaching a maximum value on March 8. Starting on this day in the lower ionospheric there was also confirmed an abnormal TEC variation over the epicenter. From March 3-11 a large increase in electron concentration was recorded at all four Japanese ground based ionosondes, which return to normal after the main earthquake. We found a positive correlation between the atmospheric and ionospheric anomalies and the Tohoku earthquake. This study may lead to a better understanding of the response of the atmosphere /ionosphere to the Great Tohoku earthquake

physics.geo-ph↗

arXiv2008

Hybrid viscosity and the magnetoviscous instability in hot, collisionless accretion disks

We aim to illustrate the role of hot protons in enhancing the magnetorotational instability (MRI) via the ``hybrid'' viscosity, which is due to the redirection of protons interacting with static magnetic field perturbations, and to establish that it is the only relevant mechanism in this situation. It has recently been shown by Balbus \cite{PBM1} and Islam & Balbus \cite{PBM11} using a fluid approach that viscous momentum transport is key to the development of the MRI in accretion disks for a wide range of parameters. However, their results do not apply in hot, advection-dominated disks, which are collisionless. We develop a fluid picture using the hybrid viscosity mechanism, that applies in the collisionless limit. We demonstrate that viscous effects arising from this mechanism can significantly enhance the growth of the MRI as long as the plasma $β\gapprox 80$. Our results facilitate for the first time a direct comparison between the MHD and quasi-kinetic treatments of the magnetoviscous instability in hot, collisionless disks.

astro-ph↗

arXiv2007

Dynamic Multiple Scattering, Frequency Shift and Possible Effects on Quasar Astronomy

The shifting of spectral lines due to induced correlation effect, discovered first by Wolf for the single scattering case which mimics the Doppler mechanism has been extended and developed further by the present authors known as Dynamic Multiple scattering(DMS). We have explored DMS theory for explaining anomalous redshifts in quasars. Our recent work, based on the statistical analysis of the Véron-Cetty data(2003) supports that quasar redshifts fit the overall Hubble expansion law, as in the case of galaxies, for z less than equal to 0.295 but not for higher redshifts, indicating clearly the inadequacy of the Doppler effect as the sole mechanism in explaining the redshifts for high redshift quasars for z greater than equal to 0.295. We found that the redshift posseses an additive, discordant component due to frequency shifting from the correlation induced mechanism which increases gradually for ~ 0.295 < z < 3.0, however, appearing to follow the evolutionary picture of the universe with absolute dependence on the physical characteristics i.e., environmental aspects of the relevant sources through which the light rays pass, after being multiply scattered.

astro-ph↗

arXiv2006

Statistical Analysis of Quasar Data and Hubble Law

The linearity of the Hubble relationship (i.e. between m and z) has been tested for galaxies and supernovea for low redshifts. We have studied this relationship for quasars for data taken from Veron Cetti Catalogue(2003).The data from Veron Cetti Catalogue for quasars appear to be truncated. The data have been analyzed using various statistical methods which are suitable for analysing the truncated data. This analysis shows lineraity (in log z) of Hubble law for very small z but non-linearity for high redshift.This will shed new light not only on the quasar astronomy but also in the cosmological debate.

astro-ph↗

arXiv2005

Anomalous Gulf Heating and Hurricane Katrinas Rapid Intensification

Global warming due to the increasing concentration of greenhouse gases has become a great concern and has been linked to increased hurricane activity associated with higher sea surface temperatures with conflicting views. Our observational results based on long term trends of sea surface temperatures reveal that the anomaly reached a record 0.8 C in the Gulf of Mexico in August 2005 as compared to previous years and may have been responsible for the intensification of the devastating Hurricane Katrina into a category 5 hurricane that hit the Southern coast of United States severely impacting the low lying city of New Orleans and the surrounding areas. In most intensifying storms, air-sea interaction is the major contributing factor and here we show how air-sea interactions might have affected Katrinas rapid intensification in the Gulf.

physics.ao-ph↗

arXiv2005

Using transport coefficients of cosmic rays in turbulent magnetic fields to determine hybrid viscosity in hot accretion disks around AGN

The nature of the viscosity operative in hot, two-temperature accretion disks around AGN has been a long-standing, unsolved problem. It has been previously suggested that protons, in conjunction with the turbulent magnetic field that is likely to exist in the accretion disk, might be crucial in providing this viscosity. Several authors have recently determined diffusion coefficients for charged particles (cosmic rays) propagating in turbulent magnetic fields by means of extensive Monte Carlo simulations. We use the diffusion coefficients for protons determined by these simulations to find the effective mean free path for protons in hot accretion disks. This in turn yields good estimates of the viscosity due to energetic protons embedded in the turbulent magnetic field of a hot, two-temperature accretion disk. We combine this with a simple two-temperature accretion disk model to determine the Shakura-Sunyaev $α$ viscosity parameter arising out of this mechanism. We find that protons diffusing in the turbulent magentic field embedded in a hot accretion d isk provide a physically reasonable source of viscosity in hot accretion disks around AGN.

astro-ph↗

arXiv2003

Geometroneurodynamics

Hilbert space structure is assumed as a valid geometric description for neurodynamics, i.e., for applying any kind of quantum formalism in brain dynamics. The orientation selectivity of the neurons is used as a justification to construct a type of statistical distance function which is proportional to the usual distance (or angle) between orientations of the neurons. The equivalence between the statistical distance and the Hilbert-space distance is discussed within this framework. It gives rise to the possibility of reanalysing the issue of measurement and information processing in the brain function

quant-ph↗

arXiv2003

Variation of Physical constants, Redshift and the Arrow of time

Theories of fundamental physics as well as cosmology must ultimately not only account for the structure and evolution of the universe and the physics of fundamental interactions, but also lead to an understanding of why this particular universe follows the physics that it does. Such theories must ultimately lead to an understanding of the values of the fundamental constants themselves. However, all such efforts have failed, leaving fundamental constants outside of any physical theories. In this paper we take a different approach than the usual evolutionary picture where the physics itself is assumed invariant. We study numerical relations among fundamental constants starting from relationships first proposed by Weinberg (1972). We have shown (Kafatos et al.2000) that they turn out to be equivalent to the relations found by Dirac (1937). Then a new scaling hypothesis relating the speed of light $c$ and the scale of the universe $R$ is explored.

astro-ph↗

arXiv2003

Quantum processes, space-time representation and brain dynamics

The recent controversy of applicability of quantum formalism to brain dynamics has been critically analysed. The prerequisites for any type of quantum formalism or quantum field theory is to investigate whether the anatomical structure of brain permits any kind of smooth geometric notion like Hilbert structure or four dimensional Minkowskian structure for quantum field theory. The present understanding of brain function clearly denies any kind of space-time representation in Minkowskian sense. However, three dimensional space and one time can be assigned to the neuromanifold and the concept of probabilistic geometry is shown to be appropriate framework to understand the brain dynamics. The possibility of quantum structure is also discussed in this framework.

quant-ph↗

arXiv2002

Sheaf Cohomology and Geometrical Approach to EPR Non-locality

A consistent geometrical approach to EPR non-locality as well as other non-local effects in QM like the Aharanov-Bohm effect, Berry phase, Gauge theories within Yang-Mills theory etc. is possible within the framework of sheaf cohomology. This sheds new light on our understanding on non-local correlations in QM, and provides a fundamental mathematical approach to fundamental problems in physics.

quant-ph↗

arXiv1999

Shift of Spectral Lines due to Dynamic Multiple Scattering and Screening Effect: Implications for Discordant Redshifts

The frequency shift of spectral lines from astronomical objects is most often explained by the Doppler Effect arising in relative motion and the broadening of a particular line is supposed to depend on the absolute temperature, pressure or the different line of sight velocities. The Wolf effect on the other hand deals with correlation induced spectral changes and explains both the broadening and shift of the spectral lines. In this framework a sufficient condition for redshift has been derived and when applicable the shift is shown to be larger than broadening. Under this condition of larger shift than broadening we find a critical source frequency below which no spectrum is analyzable for a particular medium. This gives rise to new type of screening effect which may play significant role both at laboratory scale as well as in the astronomical domain. We apply a simple interpretation of the discordant redshifts in galaxy-quasar associations.

astro-ph↗

arXiv1999

Inner region accretion flows onto black holes

We examine here the inner region accretion flows onto black holes. A variety of models are presented. We also discuss viscosity mechanisms under a variety of circumstances, for standard accretion disks onto galactic black holes and supermassive black holes and hot accretion disks. Relevant work is presented here on unified aspects of disk accretion onto supermassive black holes and the possible coupling of thick disks to beams in the inner regions. We also explore other accretion flow scenarios. We conclude that a variety of scenarios yield high temperatures in the inner flows and that viscosity is likely not higher than alpha $\sim$ 0.01.

astro-ph↗

arXiv1999

Broadening of Spectral Lines due to Dynamic Multiple Scattering and the Tully-Fisher Relation

The frequency shift of spectral lines is most often explained by the Doppler Effect in terms of relative motion, whereas the Doppler broadening of a particular line mainly depends on the absolute temperature. The Wolf effect on the other hand deals with the correlation induced spectral change and explains both the broadening and shift of the spectral lines. In this framework a relation between the width of the spectral line is related to the redshift z for the line and hence with the distance. For smaller values of z a relation similar to the Tully-Fisher relation can be obtained and for larger values of z a more general relation can be constructed. The derivation of this kind of relation based on dynamic multiple scattering theory may play a significant role in explaining the overall spectra of quasi stellar objects. We emphasize that this mechanism is not applicable for nearby galaxies, $z \leq 1$.

astro-ph↗

arXiv1996

Implications of Gamma-Ray Transparency Constraints in Blazars: Minimum Distances and Gamma-Ray Collimation

We develop a general expression for the gamma-gamma absorption coefficient for gamma-rays propagating in an arbitrary direction at an arbitrary point in space above an X-ray emitting accretion disk. The X-ray intensity is assumed to vary as a power law in energy and radius between the outer disk radius and the inner radius, which is the radius of marginal stability for a Schwarzschild black hole. We use our result for the absorption coefficient to calculate the gamma-gamma optical depth for gamma-rays created at an arbitrary height and propagating at an arbitrary angle relative to the disk axis. As an application, we use our formalism to compute the minimum distance between the central black hole and the site of production of the gamma-rays detected by EGRET during the June 1991 flare of 3C 279. Our results indicate that the ``focusing'' of the gamma-rays along the disk axis due to pair production is strong enough to explain the observed degree of alignment in blazar sources. If the gamma-rays are produced isotropically in gamma-ray blazars, then these objects should appear as bright MeV sources when viewed along off-axis lines of sight.

astro-ph↗

arXiv1996

Ion viscosity mediated by tangled Magnetic fields-An application to Black Hole Accretion disks

We derive expressions for a ``hybrid'' viscosity arising from Coulomb collisions between ions in the presence of tangled magnetic fields. Such magnetic fields are expected to be embedded in accretion flows onto black holes and other compact objects. Ion viscosity in the absence of magnetic fields has been shown to appreciable in hot accretion disks, but it was thought that the presence of the smallest of magnetic fields would effectively quench it. We show that the hybrid viscosity in hot (ion temperatures around 10^11-10^12 K) accretion disks results in values of the Shakura Sunyaev αparameter around 0.01 to 0.1-0.5. We do not model the generation of the tangled magnetic fields; we merely assume its presence and assume it to be arbitrarily strong.

astro-ph↗