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Recent documents in Physics Faculty Worksen-usWed, 11 Jan 2017 19:37:32 PST3600Plasmaspheric Plumes: Crres Observations Of Enhanced Density Beyond The Plasmapause
http://digitalcommons.lmu.edu/phys_fac/27
http://digitalcommons.lmu.edu/phys_fac/27Fri, 16 Dec 2016 11:40:53 PST
CRRES plasma wave receiver density data were used to study the distribution and properties of dense plasmaspheric-like plasma observed outside the plasmapause. Our study indicates that outer plasmaspheric structure, often called plasmaspheric plumes, blobs, tails, or detached plasma regions, can exist at all local times under all levels of geomagnetic activity. Of the 558 CRRES orbits that had at least one clearly defined plasmapause, 169 (or 30%) had plasmaspheric-like density structures at higher L shells than the plasmapause. Most of the occurrences of plasmaspheric-like plasma observed by CRRES were in the noon-to-dusk sector in the aftermath of enhanced geomagnetic activity consistent with plasmaspheric plume models.
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Jeff Sanny et al.Unparticle-Enhanced Black Holes at the LHC
http://digitalcommons.lmu.edu/phys_fac/26
http://digitalcommons.lmu.edu/phys_fac/26Fri, 16 Dec 2016 11:40:49 PST
Based on the idea that tensor unparticles can enhance the gravitational interactions between standard model particles, potential black hole formation in high energy collisions is examined. Modifications to the horizon radius rH are derived, and the corresponding geometric cross-sections of such objects are calculated. It is shown that rH increases dramatically to the electroweak scale for masses M_{BH}∼1–10 TeV, yielding a geometric cross-section σ_{BH}=πr^{2}_{H} on the order of ⩽50 pb. This suggests that unparticle physics provides a mechanism for black hole formation in future accelerators, without the requirement of extra spatial dimensions.
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Jonas R. MureikaPrimordial Black Hole Evaporation And Spontaneous Dimensional Reduction
http://digitalcommons.lmu.edu/phys_fac/25
http://digitalcommons.lmu.edu/phys_fac/25Fri, 16 Dec 2016 11:40:45 PST
Several different approaches to quantum gravity suggest the effective dimension of spacetime reduces from four to two near the Planck scale. In light of such evidence, this Letter re-examines the thermodynamics of primordial black holes (PBHs) in specific lower-dimensional gravitational models. Unlike in four dimensions, (1 + 1)-D black holes radiate with power P ∼ M^{2}_{BH}, while it is known no (2+1)-D (BTZ) black holes can exist in a non-anti-de Sitter universe. This has important relevance to the PBH population size and distribution, and consequently on cosmological evolution scenarios. The number of PBHs that have evaporated to present day is estimated, assuming they account for all dark matter. Entropy conservation during dimensional transition imposes additional constraints. If the cosmological constant is non-negative, no black holes can exist in the (2 + 1)-dimensional epoch, and consequently a (1 + 1)-dimensional black hole will evolve to become a new type of remnant. Although these results are conjectural and likely model-dependent, they open new questions about the viability of PBHs as dark matter candidates.
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Jonas R. MureikaFractal Dimensions In Perceptual Color Space: A Comparison Study Using Jackson Pollock’S Art
http://digitalcommons.lmu.edu/phys_fac/24
http://digitalcommons.lmu.edu/phys_fac/24Fri, 16 Dec 2016 11:40:41 PST
The fractal dimensions of color-specific paint patterns in various Jackson Pollock paintings are calculated using a filtering process that models perceptual response to color differences (L*a*b* color space). The advantage of the L*a*b* space filtering method over traditional red-green-blue (RGB) spaces is that the former is a perceptually uniform (metric) space, leading to a more consistent definition of “perceptually different” colors. It is determined that the RGB filtering method underestimates the perceived fractal dimension of lighter-colored patterns but not of darker ones, if the same selection criteria is applied to each. Implications of the findings to Fechner’s “principle of the aesthetic middle” and Berlyne’s work on perception of complexity are discussed.
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Jonas R. MureikaCould Any Black Holes Be Produced at the LHC?
http://digitalcommons.lmu.edu/phys_fac/23
http://digitalcommons.lmu.edu/phys_fac/23Fri, 16 Dec 2016 11:40:37 PST
We introduce analytical quantum gravity modifications of the production cross section for terascale black holes by employing an effective ultraviolet cut off l. We find the new cross sections approach the usual "black disk" form at high energy, while they differ significantly near the fundamental scale from the standard increase with respect to s. We show that the heretofore discontinuous step function used to represent the cross section threshold can realistically be modeled by two functions representing the incoming and final parton states in a high energy collision. The growth of the cross section with collision energy is thus a unique signature of l and number of spatial dimensions d. Contrary to the classical black disk result, our cross section is able to explain why black holes might not be observable in LHC experiments while they could be still at the reach of ultra-high energy cosmic ray events.
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Jonas R. Mureika et al.Constraints On Vector Unparticle Physics From Cosmic Censorship
http://digitalcommons.lmu.edu/phys_fac/22
http://digitalcommons.lmu.edu/phys_fac/22Fri, 16 Dec 2016 11:40:33 PST
Vector unparticle couplings to standard model fields produce repulsive corrections to gravity. From a general relativistic perspective, this leads to an effective Reissner-Nordstrom-like metric whose "charge" is a function of the unparticle coupling constant λ, and therefore can admit naked singularities. Requiring the system to respect cosmic censorship provides a new method of constraining the value of λ. These limits are extremely loose for stellar-mass black holes, but commensurate with existing bounds for primordial black holes. In the case of theoretical low-mass black holes, the bounds on λ are much stricter than those derived from astrophysical and accelerator phenomenology. Additional constraints on the lower limit of λ are used to estimate the mass of the smallest possible black hole M^{min}_{BH} that can be formed in the unparticle framework, as a function of the unparticle parameters (Lambda_{U};M_{U}; d_{U}; d_{BZ}).
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Jonas R. MureikaGravitationally Induced Quantum Superposition Reduction With Large Extra Dimensions
http://digitalcommons.lmu.edu/phys_fac/21
http://digitalcommons.lmu.edu/phys_fac/21Fri, 16 Dec 2016 11:40:29 PST
A gravity-driven mechanism (``objective reduction'') proposed to explain quantum state reduction is analyzed in light of the possible existence of large extra dimensions in the ADD scenario. By calculating order-of-magnitude estimates for nucleon superpositions, it is shown that if the mechanism at question is correct, constraints may be placed on the number and size of extra dimensions. Hence, measurement of superposition collapse times ({\it e.g.} through diffraction or reflection experiments) could represent a new probe of extra dimensions. The influence of a time-dependent gravitational constant on the gravity-driven collapse scheme with and without the presence of extra dimensions is also discussed.
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Jonas R. MureikaDoes Entropic Gravity Bound The Masses Of The Photon And Graviton?
http://digitalcommons.lmu.edu/phys_fac/20
http://digitalcommons.lmu.edu/phys_fac/20Fri, 16 Dec 2016 11:40:25 PST
If the information transfer between test particle and holographic screen in entropic gravity respects both the uncertainty principle and causality, a lower limit on the number of bits in the universe relative to its mass may be derived. Furthermore, these limits indicate particles that putatively travel at the speed of light -- the photon and/or graviton -- have a non-zero mass m≥10−68 kg. This result is found to be in excellent agreement with current experimental mass bounds on the graviton and photon, suggesting that entropic gravity may be the result of a (recent) softly-broken local symmetry. Stronger bounds emerge from consideration of ultradense matter such as neutron stars, yielding limits of m≥10−48−10−50 kg, barely within the experimental photon range and outside that of the graviton. We find that for black holes these criteria cannot be satisfied, and suggest some possible implications of this result.
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Jonas R. Mureika et al.The Effects Of Temperature, Humidity, And Barometric Pressure On Short-Sprint Race Times
http://digitalcommons.lmu.edu/phys_fac/19
http://digitalcommons.lmu.edu/phys_fac/19Fri, 16 Dec 2016 11:40:21 PST
A numerical model of 100 m and 200 m world class sprinting performances is modified using standard hydrodynamic principles to include effects of air temperature, pressure, and humidity levels on aerodynamic drag. The magnitude of the effects are found to be dependent on wind speed. This implies that differing atmospheric conditions can yield slightly different corrections for the same wind gauge reading. In the absence of wind, temperature is found to induce the largest variation in times (0.01 s per 10◦C increment in the 100 m), while relative humidity contributes the least (under 0.01 s for all realistic conditions for 100 m). Barometric pressure variations at a particular venue can also introduce fluctuations in performance times on the order of a 0.01 s for this race. The combination of all three variables is essentially additive, and is more important for headwind conditions that for tail-winds. As expected, calculated corrections in the 200 m are 1 magnified due to the longer duration of the race. The overall effects of these factors on sprint times can be considered a “second order” adjustment to previous methods which rely strictly on a venue’s physical elevation, but can become important in extreme conditions.
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Jonas R. MureikaInterpreting Force Concept Inventory Scores: NormalizedGain and SAT Scores
http://digitalcommons.lmu.edu/phys_fac/28
http://digitalcommons.lmu.edu/phys_fac/28Fri, 16 Dec 2016 11:25:23 PST
Preinstruction SAT scores and normalized gains (G) on the force concept inventory (FCI) were examined for individual students in interactive engagement (IE) courses in introductory mechanics at one high school (N=335) and one university (N=292), and strong, positive correlations were found for both populations (r=0.57 and r=0.46, respectively). These correlations are likely due to the importance of cognitive skills and abstract reasoning in learning physics. The larger correlation coefficient for the high school population may be a result of the much shorter time interval between taking the SAT and studying mechanics, because the SAT may provide a more current measure of abilities when high school students begin the study of mechanics than it does for college students, who begin mechanics years after the test is taken. In prior research a strong correlation between FCI G and scores on Lawson's Classroom Test of Scientific Reasoning for students from the same two schools was observed. Our results suggest that, when interpreting class average normalized FCI gains and comparing different classes, it is important to take into account the variation of students' cognitive skills, as measured either by the SAT or by Lawson's test. While Lawson's test is not commonly given to students in most introductory mechanics courses, SAT scores provide a readily available alternative means of taking account of students' reasoning abilities. Knowing the students' cognitive level before instruction also allows one to alter instruction or to use an intervention designed to improve students' cognitive level.
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Vincent P. Coletta et al.Intonation and Compensation of Fretted String Instruments
http://digitalcommons.lmu.edu/phys_fac/18
http://digitalcommons.lmu.edu/phys_fac/18Fri, 28 Oct 2016 17:08:24 PDT
We discuss theoretical and physical models that are useful for analyzing the intonation of musical instruments such as guitars and mandolins and can be used to improve the tuning on these instruments. The placement of frets on the fingerboard is designed according to mathematical rules and the assumption of an ideal string. The analysis becomes more complicated when we include the effects of deformation of the string and inharmonicity due to other string characteristics. As a consequence, perfect intonation of all the notes on the instrument cannot be achieved, but complex compensation procedures can be introduced to minimize the problem. To test the validity of these procedures, we performed extensive measurements using standard monochord sonometers and other acoustical devices, confirming the correctness of our theoreticalmodels. These experimental activities can be integrated into acoustics courses and laboratories and can become a more advanced version of basic experiments with monochords and sonometers.
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Gabriele U. Varieschi et al.Toy Blocks and Rotational Physics
http://digitalcommons.lmu.edu/phys_fac/17
http://digitalcommons.lmu.edu/phys_fac/17Fri, 28 Oct 2016 17:08:18 PDT
Have you ever observed a child playing with toy blocks? A favorite game is to build towers and then make them topple like falling trees. To the eye of a trained physicist this should immediately look like an example of the physics of “falling chimneys,” when tall structures bend and break in mid-air while falling to the ground. The game played with toy blocks can actually reproduce well what is usually seen in photographs of falling towers, such as the one that appeared on the cover of the September 1976 issue of The Physics Teacher.1 In this paper we describe how we performed and analyzed these simple but interesting experiments with toy blocks.
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Gabriele U. Varieschi et al.Toy Models for the Falling Chimney
http://digitalcommons.lmu.edu/phys_fac/16
http://digitalcommons.lmu.edu/phys_fac/16Fri, 28 Oct 2016 17:08:11 PDT
In this paper we review the theory of the ‘‘falling chimney,’’ which deals with the breaking in mid-air of tall structures when they fall to the ground. We show that these ruptures can be caused by either shear forces typically developing near the base, or by the bending of the structure which is caused primarily by the internal bending moment. In the latter case the breaking is more likely to occur between one-third and one-half of the height of the chimney. Small scale toy models are used to reproduce the dynamics of the falling chimney. By examining photos taken during the fall of these models we test the adequacy of the theory. This type of experiment, which is easy to perform and conceptually challenging, can become part of a rotational mechanics lab for undergraduate students.
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Gabriele U. Varieschi et al.Wormhole Geometries in Fourth-Order Conformal Weyl Gravity
http://digitalcommons.lmu.edu/phys_fac/15
http://digitalcommons.lmu.edu/phys_fac/15Thu, 14 Jul 2016 16:21:40 PDT
We present an analysis of the classic wormhole geometries based on conformal Weyl gravity, rather than standard general relativity. The main characteristics of the resulting traversable wormholes remain the same as in the seminal study by Morris and Thorne, namely, that effective super-luminal motion is a viable consequence of the metric. Improving on previous work on the subject, we show that for particular choices of the shape and redshift functions the wormhole metric in the context of conformal gravity does not violate the main energy conditions at or near the wormhole throat. Some exotic matter might still be needed at the junction between our solutions and flat spacetime, but we demonstrate that the averaged null energy condition (as evaluated along radial null geodesics) is satisfied for a particular set of wormhole geometries. Therefore, if fourth-order conformal Weyl gravity is a correct extension of general relativity, traversable wormholes might become a realistic solution for interstellar travel.
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Gabriele U. Varieschi et al.Astrophysical Tests of Kinematical Conformal Cosmology in Fourth-Order Conformal Weyl Gravity
http://digitalcommons.lmu.edu/phys_fac/14
http://digitalcommons.lmu.edu/phys_fac/14Thu, 14 Jul 2016 16:21:33 PDT
In this work we analyze kinematical conformal cosmology (KCC), an alternative cosmological model based on conformal Weyl gravity (CG), and test it against current type Ia supernova (SNIa) luminosity data and other astrophysical observations. Expanding upon previous work on the subject, we revise the analysis of SNIa data, confirming that KCC can explain the evidence for an accelerating expansion of the Universe without using dark energy or other exotic components. We obtain an independent evaluation of the Hubble constant, H0 = 67:53 kms-1 Mpc-1, very close to the current best estimates. The main KCC and CG parameters are re-evaluated and their revised values are found to be close to previous estimates. We also show that available data for the Hubble parameter as a function of redshift can be fitted using KCC and that this model does not suffer from any apparent age problem. Overall, KCC remains a viable alternative cosmological model, worthy of further investigation.
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Gabriele U. VarieschiKerr Metric, Geodesic Motion, and Flyby Anomaly in Fourth-Order Conformal Gravity
http://digitalcommons.lmu.edu/phys_fac/13
http://digitalcommons.lmu.edu/phys_fac/13Thu, 14 Jul 2016 16:21:27 PDT
In this paper we analyze the Kerr geometry in the context of Conformal Gravity, an alternative theory of gravitation, which is a direct extension of General Relativity (GR). Following previous studies in the literature, we introduce an explicit expression of the Kerr metric in Conformal Gravity, which naturally reduces to the standard GR Kerr geometry in the absence of Conformal Gravity effects. As in the standard case, we show that the Hamilton–Jacobi equation governing geodesic motion in a space-time based on this geometry is indeed separable and that a fourth constant of motion—similar to Carter’s constant—can also be introduced in Conformal Gravity. Consequently, we derive the fundamental equations of geodesic motion and show that the problem of solving these equations can be reduced to one of quadratures. In particular, we study the resulting time-like geodesics in Conformal Gravity Kerr geometry by numerically integrating the equations of motion for Earth flyby trajectories of spacecraft. We then compare our results with the existing data of the Flyby Anomaly in order to ascertain whether Conformal Gravity corrections are possibly the origin of this gravitational anomaly. Although Conformal Gravity slightly affects the trajectories of geodesic motion around a rotating spherical object, we show that these corrections are minimal and are not expected to be the origin of the Flyby Anomaly, unless conformal parameters are drastically different from current estimates. Therefore, our results confirm previous analyses, showing that modifications due to Conformal Gravity are not likely to be detected at the Solar System level, but might affect gravity at the galactic or cosmological scale.
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Gabriele U. VarieschiSimulating a Guitar with a Conventional Sonometer
http://digitalcommons.lmu.edu/phys_fac/12
http://digitalcommons.lmu.edu/phys_fac/12Thu, 14 Jul 2016 16:21:20 PDT
In this paper we present a simple way to convert a conventional sonometer into a simulated fretted instrument, such as a guitar or similar, by adding a fingerboard to the sonometer. In particular, we use this modified apparatus in relation to the problem of the instrument intonation, i.e., how to obtain correctly tuned notes on these string instruments. The experimental procedures presented in this study can become a more structured laboratory activity to be used in general physics courses or acoustics classes.
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Zily Burstein et al.Conformal Gravity and the Alcubierre Warp Drive Metric
http://digitalcommons.lmu.edu/phys_fac/11
http://digitalcommons.lmu.edu/phys_fac/11Thu, 14 Jul 2016 16:21:14 PDT
We present an analysis of the classic Alcubierre metric based on conformal gravity, rather than standard general relativity. The main characteristics of the resulting warp drive remain the same as in the original study by Alcubierre, that is, effective superluminal motion is a viable outcome of the metric. We show that for particular choices of the shaping function, the Alcubierre metric in the context of conformal gravity does not violate the weak energy condition, as was the case of the original solution. In particular, the resulting warp drive does not require the use of exotic matter. Therefore, if conformal gravity is a correct extension of general relativity, superluminal motion via an Alcubierre metric might be a realistic solution, thus allowing faster-than-light interstellar travel.
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Gabriele U. Varieschi et al.Prompt Atmospheric Neutrinos and Muons: NLO versus LO QCD Predictions
http://digitalcommons.lmu.edu/phys_fac/10
http://digitalcommons.lmu.edu/phys_fac/10Thu, 07 Nov 2013 18:25:24 PSTGabriele U. VarieschiConformal Cosmology and the Pioneer Anomaly
http://digitalcommons.lmu.edu/phys_fac/9
http://digitalcommons.lmu.edu/phys_fac/9Thu, 07 Nov 2013 18:20:38 PSTGabriele U. Varieschi