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Articles 1 - 30 of 67
Full-Text Articles in Entire DC Network
Discovery Of Extensive Optical Emission Associated With The X-Ray Bright, Radio Faint Galactic Snr G156.2+5.7, Christopher L. Gerardy, Robert A. Fesen
Discovery Of Extensive Optical Emission Associated With The X-Ray Bright, Radio Faint Galactic Snr G156.2+5.7, Christopher L. Gerardy, Robert A. Fesen
Dartmouth Scholarship
We present wide‐field Hα images of the Galactic supernova remnant (SNR) G156.2+5.7 which reveal the presence of considerable faint Hα line emission coincident with the remnant's X‐ray emission. We also present low‐resolution optical spectra for a few representative emission regions. The outermost Hα emission consists largely of long and thin (unresolved), smoothly curved filaments of Balmer‐dominated emission presumably associated with the remnant's forward shock front. Patches of brighter Hα emission along the western, south‐central, and north‐eastern regions appear to be radiative shocked interstellar medium filaments like those commonly seen in SNRs, with relatively strong [O i]λλ6300, 6364 and [S ii]λλ6716, …
Small-Scale Turbulence In A Closed-Field-Line Geometry, Paolo Ricci, B. N. Rogers, W. Dorland
Small-Scale Turbulence In A Closed-Field-Line Geometry, Paolo Ricci, B. N. Rogers, W. Dorland
Dartmouth Scholarship
Plasma turbulence due to small-scale entropy modes is studied with gyrokinetic simulations in a simple closed-field-line geometry, the Z pinch, in low-β parameter regimes that are stable to ideal interchange modes. We find an enormous variation in the nonlinear dynamics and particle transport as a function of two main parameters, the density gradient and the plasma collisionality. This variation is explained in part by the damping and stability properties of spontaneously formed zonal flows in the system. As in toroidal systems, the zonal flows can lead to a strong nonlinear suppression of transport below a critical gradient that is determined …
Small-Scale Structures In Three-Dimensional Magnetohydrodynamic Turbulence, P. D. Mininni, A. G. Pouquet, D. C. Montgomery
Small-Scale Structures In Three-Dimensional Magnetohydrodynamic Turbulence, P. D. Mininni, A. G. Pouquet, D. C. Montgomery
Dartmouth Scholarship
We investigate using direct numerical simulations with grids up to 15363 points, the rate at which small scales develop in a decaying three-dimensional MHD flow both for deterministic and random initial conditions. Parallel current and vorticity sheets form at the same spatial locations, and further destabilize and fold or roll up after an initial exponential phase. At high Reynolds numbers, a self-similar evolution of the current and vorticity maxima is found, in which they grow as a cubic power of time; the flow then reaches a finite dissipation rate independent of the Reynolds number.
Cheating To Get Better Roommates In A Random Stable Matching, Chien-Chung Huang
Cheating To Get Better Roommates In A Random Stable Matching, Chien-Chung Huang
Computer Science Technical Reports
This paper addresses strategies for the stable roommates problem, assuming that a stable matching is chosen at random. We investigate how a cheating man should permute his preference list so that he has a higher-ranking roommate probabilistically. In the first part of the paper, we identify a necessary condition for creating a new stable roommate for the cheating man. This condition precludes any possibility of his getting a new roommate ranking higher than all his stable roommates when everyone is truthful. Generalizing to the case that multiple men collude, we derive another impossibility result: given any stable matching in which …
Evaluating Next Cell Predictors With Extensive Wi-Fi Mobility Data, Libo Song, David Kotz, Ravi Jain, Xiaoning He
Evaluating Next Cell Predictors With Extensive Wi-Fi Mobility Data, Libo Song, David Kotz, Ravi Jain, Xiaoning He
Dartmouth Scholarship
Location is an important feature for many applications, and wireless networks can better serve their clients by anticipating client mobility. As a result, many location predictors have been proposed in the literature, though few have been evaluated with empirical evidence. This paper reports on the results of the first extensive empirical evaluation of location predictors, using a two-year trace of the mobility patterns of over 6,000 users on Dartmouth's campus-wide Wi-Fi wireless network. The surprising results provide critical evidence for anyone designing or using mobility predictors. \par We implemented and compared the prediction accuracy of several location predictors drawn from …
Structured Waves Near The Plasma Frequency Observed In Three Auroral Rocket Flights, M Samara, J Labelle
Structured Waves Near The Plasma Frequency Observed In Three Auroral Rocket Flights, M Samara, J Labelle
Dartmouth Scholarship
Abstract. We present observations of waves at and just above the plasma frequency (fpe) from three high frequency electric field experiments on three recent rockets launched to altitudes of 300–900 km in active aurora. The predominant observed HF waves just above fpe are narrowband, short- lived emissions with amplitudes ranging from <1mV/m to 20 mV/m, often associated with structured electron den- sity. The nature of these HF waves, as determined from frequency-time spectrograms, is highly variable: in some cases, the frequency decreases monotonically with time as in the “HF-chirps” previously reported (McAdams and La- Belle, 1999), but in other cases rising frequencies are ob- served, or features which alternately rise and fall in fre- quency. They exhibit two timescales of amplitude variation: a short timescale, typically 50–100 ms, associated with in- dividual discrete features, and a longer timescale associated with the general decrease in the amplitudes of the emissions as the rocket moves away from where the condition f ∼fpe holds. The latter timescale ranges from 0.6 to 6.0 s, corre- sponding to distances of 2–7 km, assuming the phenomenon to be stationary and using the rocket velocity to convert time to distance.
Single-Bit Feedback And Quantum-Dynamical Decoupling, Francesco Ticozzi, Lorenza Viola
Single-Bit Feedback And Quantum-Dynamical Decoupling, Francesco Ticozzi, Lorenza Viola
Dartmouth Scholarship
Synthesizing an effective identity evolution in a target system subjected to unwanted unitary or nonunitary dynamics is a fundamental task for both quantum control and quantum information processing applications. Here, we investigate how single-bit, discrete-time feedback capabilities may be exploited to enact or to enhance quantum procedures for effectively suppressing unwanted dynamics in a finite-dimensional open quantum system. An explicit characterization of the joint unitary propagators correctable by a single-bit feedback strategy for arbitrary evolution time is obtained. For a two-dimensional target system, we show how by appropriately combining quantum feedback with dynamical decoupling methods, concatenated feedback-decoupling schemes may be …
The Asymmetric Explosion Of Type Ia Supernovae As Seen From Near-Infrared Observations, Kentaro Motohara, Keiichi Maeda, Christopher L. Gerardy, Ken'ichi Nomoto, Masaomi Tanaka, Nozomu Tominaga, Takuya Ohkubo, Paolo A. Mazzali, Robert A. Fesen, Peter Hoflich, J. Craig Wheeler
The Asymmetric Explosion Of Type Ia Supernovae As Seen From Near-Infrared Observations, Kentaro Motohara, Keiichi Maeda, Christopher L. Gerardy, Ken'ichi Nomoto, Masaomi Tanaka, Nozomu Tominaga, Takuya Ohkubo, Paolo A. Mazzali, Robert A. Fesen, Peter Hoflich, J. Craig Wheeler
Dartmouth Scholarship
We present near-infrared spectra of late-phase (>200 days) Type Ia supernovae (SNe Ia) taken at the Subaru Telescope. The [Fe II] line of SN 2003hv shows a clear flat-topped feature, while that of SN 2005W shows a less prominent flatness. In addition, a large shift in their line center, varying from -3000 to 1000 km s-1 with respect to the host galaxies, is seen. Such a shift suggests the occurrence of an off-center, nonspherical explosion in the central region and provides important, new constraints on the explosion models of SNe Ia.
Decoherence And Recoherence In A Vibrating Rf Squid, Eyal Buks, M. P. Blencowe
Decoherence And Recoherence In A Vibrating Rf Squid, Eyal Buks, M. P. Blencowe
Dartmouth Scholarship
We study an rf SQUID, in which a section of the loop is a freely suspended beam that is allowed to oscillate mechanically. The coupling between the rf SQUID and the mechanical resonator originates from the dependence of the total magnetic flux threading the loop on the displacement of the resonator. Motion of the latter affects the visibility of Rabi oscillations between the two lowest energy states of the rf SQUID. We address the feasibility of experimental observation of decoherence and recoherence, namely decay and rise of the visibility, in such a system.
Spitzer Measurements Of Atomic And Molecular Abundances In The Type Iip Sn 2005af, Rubina Kotak, Peter Meikle, Monica Pozzo, Schuyler D. Van Dyk, Duncan Farrah, Robert Fesen, Alexei V. Filippenko, Ryan J. Foley, Claes Fransson, Christopher L. Gerardy, Peter A. Hoflich, Peter Lundqvist, Seppo Mattila, Jesper Sollerman, J. Craig Wheeler
Spitzer Measurements Of Atomic And Molecular Abundances In The Type Iip Sn 2005af, Rubina Kotak, Peter Meikle, Monica Pozzo, Schuyler D. Van Dyk, Duncan Farrah, Robert Fesen, Alexei V. Filippenko, Ryan J. Foley, Claes Fransson, Christopher L. Gerardy, Peter A. Hoflich, Peter Lundqvist, Seppo Mattila, Jesper Sollerman, J. Craig Wheeler
Dartmouth Scholarship
We present results based on mid-infrared (3.6-30 μm) observations with the Spitzer Space Telescope of the nearby Type IIP supernova 2005af. We report the first ever detection of the SiO molecule in a Type IIP supernova. Together with the detection of the CO fundamental, this is an exciting finding as it may signal the onset of dust condensation in the ejecta. From a wealth of fine-structure lines we provide abundance estimates for stable Ni, Ar, and Ne that, via spectral synthesis, may be used to constrain nucleosynthesis models.
Casimir Forces And Non-Newtonian Gravitation, Roberto Onofrio
Casimir Forces And Non-Newtonian Gravitation, Roberto Onofrio
Dartmouth Scholarship
The search for non-relativistic deviations from Newtonian gravitation can lead to new phenomena signalling the unification of gravity with the other fundamental interactions. Various recent theoretical frameworks indicate a possible window for non-Newtonian forces with gravitational coupling strength in the micrometre range. The major expected background in the same range is attributable to the Casimir force or variants of it if dielectric materials, rather than conducting ones, are considered. Here we review the measurements of the Casimir force performed so far in the micrometre range and how they determine constraints on non-Newtonian gravitation, also discussing the dominant sources of false …
The Young Open Cluster Ngc 2129, Giovanni Carraro, Brian Chaboyer, James Perencevich
The Young Open Cluster Ngc 2129, Giovanni Carraro, Brian Chaboyer, James Perencevich
Dartmouth Scholarship
The first charge‐coupled device UBV(RI)C photometric study in the area of the doubtful open cluster NGC 2129 is presented. Photometry of a field offset 15 arcmin northwards is also provided, to probe the Galactic disc population towards the cluster. Using star counts, proper motions from the UCAC2 catalogue, colour–magnitude and colour–colour diagrams, we demonstrate that NGC 2129 is a young open cluster. The cluster radius is 2.5 arcmin, and across this region we find evidence of significant differential reddening, although the reddening law seems to be normal towards its direction. Updated estimates of the cluster fundamental …
Generalized Entanglement As A Natural Framework For Exploring Quantum Chaos, Y. S. Weinstein, L Viola
Generalized Entanglement As A Natural Framework For Exploring Quantum Chaos, Y. S. Weinstein, L Viola
Dartmouth Scholarship
We demonstrate that generalized entanglement (Barnum et al., Phys. Rev. A, 68 (2003) 032308) provides a natural and reliable indicator of quantum chaotic behavior. Since generalized entanglement depends directly on a choice of preferred observables, exploring how generalized entanglement increases under dynamical evolution is possible without invoking an auxiliary coupled system or decomposing the system into arbitrary subsystems. We find that, in the chaotic regime, the long-time saturation value of generalized entanglement agrees with random matrix theory predictions. For our system, we provide physical intuition into generalized entanglement within a single system by invoking the notion of extent …
Enhanced Convergence And Robust Performance Of Randomized Dynamical Decoupling, Lea F. Santos, Lorenza Viola
Enhanced Convergence And Robust Performance Of Randomized Dynamical Decoupling, Lea F. Santos, Lorenza Viola
Dartmouth Scholarship
We demonstrate the advantages of randomization in coherent quantum dynamical control. For systems which are either time-varying or require decoupling cycles involving a large number of operations, we find that simple randomized protocols offer superior convergence and stability as compared to deterministic counterparts. In addition, we show how randomization may allow us to outperform purely deterministic schemes at long times, including combinatorial and concatenated methods. General criteria for optimally interpolating between deterministic and stochastic design are proposed and illustrated in explicit decoupling scenarios relevant to quantum information storage.
The Zeta Function Of A Hypergraph, Christopher K. Storm
The Zeta Function Of A Hypergraph, Christopher K. Storm
Dartmouth Scholarship
We generalize the Ihara-Selberg zeta function to hypergraphs in a natural way. Hashimoto's factorization results for biregular bipartite graphs apply, leading to exact factorizations. For $(d,r)$-regular hypergraphs, we show that a modified Riemann hypothesis is true if and only if the hypergraph is Ramanujan in the sense of Winnie Li and Patrick Solé. Finally, we give an example to show how the generalized zeta function can be applied to graphs to distinguish non-isomorphic graphs with the same Ihara-Selberg zeta function.
Compressional Mode Softening And Euler Buckling Patterns In Mesoscopic Beams, W. E. Lawrence, M. N. Wybourne, S. M. Carr
Compressional Mode Softening And Euler Buckling Patterns In Mesoscopic Beams, W. E. Lawrence, M. N. Wybourne, S. M. Carr
Dartmouth Scholarship
We describe a sequence of Euler buckling instabilities associated with the transverse modes of a mesoscopic beam subjected to compressional strain. As the strain is increased, successively higher normal mode frequencies are driven to zero; each zero signals an instability in the corresponding normal mode that can be realized if all lower instabilities are suppressed by constraints. When expressed in terms of the critical buckling modes, the potential energy functional takes the form of a multimode Ginzburg–Landau system that describes static equilibria in the presence of symmetry breaking forces. This model is used to analyse the complex equilibrium shapes that …
The Microstructure Of Meteoric Ice From Vostok, Antarctica, Rachel Obbard, Ian Baker
The Microstructure Of Meteoric Ice From Vostok, Antarctica, Rachel Obbard, Ian Baker
Dartmouth Scholarship
The 3623 m long, 5G core collected at Vostok station, Antarctica, contains alternating layers of meteoric ice with two distinctly different microstructures. In this paper, we present the microstructure and impurity content of a number of specimens ranging in depth from 97 to 3416 m, describe in detail the characteristics of the different layers and propose a mechanism for their microstructural development. Digital image analysis, ion chromatography, scanning electron microscopy and energy dispersive X-ray spectroscopy were used to measure texture and the location and type of impurities; electron backscatter diffraction was used to determine crystal orientation. The ice associated with …
Mobicom Poster Abstract: Bandwidth Reservation Using Wlan Handoff Prediction, Libo Song, Udayan Deshpande, Ulaş C. Kozat, David Kotz, Ravi Jain
Mobicom Poster Abstract: Bandwidth Reservation Using Wlan Handoff Prediction, Libo Song, Udayan Deshpande, Ulaş C. Kozat, David Kotz, Ravi Jain
Dartmouth Scholarship
Many network services may be improved or enabled by successful predictions of users' future mobility. The success of predictions depend on how much accuracy can be achieved on real data and on the sensitivity of particular applications to this achievable accuracy. We investigate these issues for the case of advanced bandwidth reservation using real WLAN traces collected on the Dartmouth College campus.
A Spitzer Space Telescope Study Of Sn 2002hh: An Infrared Echo From A Type Iip Supernova, W. P. S. Meikle, S. Mattila, C. L. Gerardy, R. Kotak, M. Pozzo, S. D. Van Dyk, D. Farrah, R. A. Fesen
A Spitzer Space Telescope Study Of Sn 2002hh: An Infrared Echo From A Type Iip Supernova, W. P. S. Meikle, S. Mattila, C. L. Gerardy, R. Kotak, M. Pozzo, S. D. Van Dyk, D. Farrah, R. A. Fesen
Dartmouth Scholarship
We present late-time (590-994 days) mid-IR photometry of the normal but highly reddened Type IIP supernova SN 2002hh. Bright, cool, slowly fading emission is detected from the direction of the supernova. Most of this flux appears not to be driven by the supernova event but instead probably originates in a cool, obscured star formation region or molecular cloud along the line of sight. We also show, however, that the declining component of the flux is consistent with an SN-powered IR echo from a dusty progenitor CSM. Mid-IR emission could also be coming from newly condensed dust and/or an ejecta/CSM impact, …
Digital Image Ballistics From Jpeg Quantization, Hany Farid
Digital Image Ballistics From Jpeg Quantization, Hany Farid
Computer Science Technical Reports
Most digital cameras export images in the JPEG file format. This lossy compression scheme employs a quantization table that controls the amount of compression achieved. Different cameras typically employ different tables. A comparison of an image's quantization scheme to a database of known cameras affords a simple technique for confirming or denying an image's source. Similarly, comparison to a database of photo-editing software can be used in a forensic setting to determine if an image was edited after its original recording.
Tools And Algorithms To Advance Interactive Intrusion Analysis Via Machine Learning And Information Retrieval, Javed Aslam, Sergey Bratus, Virgil Pavlu
Tools And Algorithms To Advance Interactive Intrusion Analysis Via Machine Learning And Information Retrieval, Javed Aslam, Sergey Bratus, Virgil Pavlu
Computer Science Technical Reports
We consider typical tasks that arise in the intrusion analysis of log data from the perspectives of Machine Learning and Information Retrieval, and we study a number of data organization and interactive learning techniques to improve the analyst's efficiency. In doing so, we attempt to translate intrusion analysis problems into the language of the abovementioned disciplines and to offer metrics to evaluate the effect of proposed techniques. The Kerf toolkit contains prototype implementations of these techniques, as well as data transformation tools that help bridge the gap between the real world log data formats and the ML and IR data …
Lowness And Π Nullsets, Rod Downey, Andre Nies, Rebecca Weber, Liang Yu
Lowness And Π Nullsets, Rod Downey, Andre Nies, Rebecca Weber, Liang Yu
Dartmouth Scholarship
We prove that there exists a noncomputable c.e. real which is low for weak 2-randomness, a definition of randomness due to Kurtz, and that all reals which are low for weak 2-randomness are low for Martin-Lof randomness.
Quantum Entanglement Via Nilpotent Polynomials, Aikaterini Mandilara, Vladimir M. Akulin, Andrei V. Smilga, Lorenza Viola
Quantum Entanglement Via Nilpotent Polynomials, Aikaterini Mandilara, Vladimir M. Akulin, Andrei V. Smilga, Lorenza Viola
Dartmouth Scholarship
We propose a general method for introducing extensive characteristics of quantum entanglement. The method relies on polynomials of nilpotent raising operators that create entangled states acting on a reference vacuum state. By introducing the notion of tanglemeter, the logarithm of the state vector represented in a special canonical form and expressed via polynomials of nilpotent variables, we show how this description provides a simple criterion for entanglement as well as a universal method for constructing the invariants characterizing entanglement. We compare the existing measures and classes of entanglement with those emerging from our approach. We derive the equation of motion …
Heliospheric Response To Different Possible Interstellar Environments, Hans-Reinhard Muller, Priscilla C. Frisch, Vladimir Florinski, Gary P. Zank
Heliospheric Response To Different Possible Interstellar Environments, Hans-Reinhard Muller, Priscilla C. Frisch, Vladimir Florinski, Gary P. Zank
Dartmouth Scholarship
At present, the heliosphere is embedded in a warm, low-density interstellar cloud that belongs to a cloud system flowing through the local standard of rest with a velocity near ~18 km s-1. The velocity structure of the nearest interstellar material (ISM), combined with theoretical models of the local interstellar cloud (LIC), suggest that the Sun passes through cloudlets on timescales of ≤103-104 yr, so the heliosphere has been, and will be, exposed to different interstellar environments over time. By means of a multifluid model that treats plasma and neutral hydrogen self-consistently, the interaction of the …
Metric Measurements On A Plane From A Single Image, Micah K. Johnson, Hany Farid
Metric Measurements On A Plane From A Single Image, Micah K. Johnson, Hany Farid
Computer Science Technical Reports
The past decade has seen considerable advances in the application of principles from projective geometry to problems in image analysis and computer vision. In this paper, we review a subset of this work, and leverage these results for the purpose of forensic analysis. Specifically, we review three techniques for making metric measurements on planar surfaces from a single image. The resulting techniques should prove useful in forensic settings where real-world measurements are required.
Exact Casimir Interaction Between Eccentric Cylinders, D. A. R. Dalvit, F. C. Lombardo, F. D. Mazzitelli, R. Onofrio
Exact Casimir Interaction Between Eccentric Cylinders, D. A. R. Dalvit, F. C. Lombardo, F. D. Mazzitelli, R. Onofrio
Dartmouth Scholarship
The Casimir force is the ultimate background in ongoing searches for extragravitational forces in the micrometer range. Eccentric cylinders offer favorable experimental conditions for such measurements as spurious gravitational and electrostatic effects can be minimized. Here we report on the evaluation of the exact Casimir interaction between perfectly conducting eccentric cylinders using a mode summation technique, and study different limiting cases of relevance for Casimir force measurements, with potential implications for the understanding of mechanical properties of nanotubes.
Sampled: Shared Anonymous Music Playback Using Wireless Devices, Constantinos Neophytou
Sampled: Shared Anonymous Music Playback Using Wireless Devices, Constantinos Neophytou
Computer Science Technical Reports
Recent advances in mobile computing enable many new applications, yet at the same time create privacy implications caused by the increasing amount of data that becomes available. This thesis will explore the possibilities of wireless-enabled portable devices and their attending privacy implications. We will describe how such a device containing personal information about the musical preferences of its user can help improve the user's experience in a social setting where music is played for all, and at the same time preserve each user's privacy.
Wait-Free And Obstruction-Free Snapshot, Khanh Do Ba
Wait-Free And Obstruction-Free Snapshot, Khanh Do Ba
Dartmouth College Undergraduate Theses
The snapshot problem was first proposed over a decade ago and has since been well-studied in the distributed algorithms community. The challenge is to design a data structure consisting of $m$ components, shared by upto $n$ concurrent processes, that supports two operations. The first, $Update(i,v)$, atomically writes $v$ to the $i$th component. The second, $Scan()$, returns an atomic snapshot of all $m$ components. We consider two termination properties: wait-freedom, which requires a process to always terminate in a bounded number of its own steps, and the weaker obstruction-freedom, which requires such termination only for processes that eventually execute uninterrupted. First, …
Computation Reuse In Statics And Dynamics Problems For Assemblies Of Rigid Bodies, Anne Loomis
Computation Reuse In Statics And Dynamics Problems For Assemblies Of Rigid Bodies, Anne Loomis
Dartmouth College Master’s Theses
The problem of determining the forces among contacting rigid bodies is fundamental to many areas of robotics, including manipulation planning, control, and dynamic simulation. For example, consider the question of how to unstack an assembly, or how to find stable regions of a rubble pile. In considering problems of this type over discrete or continuous time, we often encounter a sequence of problems with similar substructure. The primary contribution of our work is the observation that in many cases, common physical structure can be exploited to solve a sequence of related problems more efficiently than if each problem were considered …
Grb 060218/Sn 2006aj: A Gamma-Ray Burst And Prompt Supernova Atz= 0.0335, N. Mirabal, J. P. Halpern, D. An, J. R. Thorstensen, D. M. Terndrup
Grb 060218/Sn 2006aj: A Gamma-Ray Burst And Prompt Supernova Atz= 0.0335, N. Mirabal, J. P. Halpern, D. An, J. R. Thorstensen, D. M. Terndrup
Dartmouth Scholarship
We report the imaging and spectroscopic localization of GRB 060218 to a low-metallicity dwarf starburst galaxy at z = 0.03345 ± 0.00006. In addition to making it the second nearest gamma-ray burst known, optical spectroscopy reveals the earliest detection of weak, supernova-like Si II near 5720 Å (~0.1c), starting 1.95 days after the burst trigger. UBVRI photometry obtained between 1 and 26 days postburst confirms the early rise of supernova light, and suggests a short time delay between the gamma-ray burst and the onset of SN 2006aj if the early appearance of a soft component in the X-ray …