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MIT Open Access Articles

Mostrando recursos 1 - 20 de 22.998

  1. Strengthened Monotonicity of Relative Entropy via Pinched Petz Recovery Map

    Sutter, David; Tomamichel, Marco; Harrow, Aram W
    The quantum relative entropy between two states satisfies a monotonicity property meaning that applying the same quantum channel to both states can never increase their relative entropy. It is known that this inequality is only tight when there is a recovery map that exactly reverses the effects of the quantum channel on both states. In this paper, we strengthen this inequality by showing that the difference of relative entropies is bounded below by the measured relative entropy between the first state and a recovered state from its processed version. The recovery map is a convex combination of rotated Petz recovery...

  2. Collective antibiotic resistance: mechanisms and implications

    Vega, Nicole; Gore, Jeff
    In collective resistance, microbial communities are able to survive antibiotic exposures that would be lethal to individual cells. In this review, we explore recent advances in understanding collective resistance in bacteria. The population dynamics of ‘cheating’ in a system with cooperative antibiotic inactivation have been described, providing insight into the demographic factors that determine resistance allele frequency in bacteria. Extensive work has elucidated mechanisms underlying collective resistance in biofilms and addressed questions about the role of cooperation in these structures. Additionally, recent investigations of ‘bet-hedging’ strategies in bacteria have explored the contributions of stochasticity and regulation to bacterial phenotypic heterogeneity...

  3. Slower recovery in space before collapse of connected populations

    Dai, Lei; Korolev, Kirill Sergeevich; Gore, Jeff
    Slower recovery from perturbations near a tipping point and its indirect signatures in fluctuation patterns have been suggested to foreshadow catastrophes in a wide variety of systems. Recent studies of populations in the field and in the laboratory have used time-series data to confirm some of the theoretically predicted early warning indicators, such as an increase in recovery time or in the size and timescale of fluctuations. However, the predictive power of temporal warning signals is limited by the demand for long-term observations. Large-scale spatial data are more accessible, but the performance of warning signals in spatially extended systems needs...

  4. Competition between species can stabilize public-goods cooperation within a species

    Celiker, Hasan; Gore, Jeff
    Competition between species is a major ecological force that can drive evolution. Here, we test the effect of this force on the evolution of cooperation within a species. We use sucrose metabolism of budding yeast, Saccharomyces cerevisiae, as a model cooperative system that is subject to social parasitism by cheater strategies. We find that when cocultured with a bacterial competitor, Escherichia coli, the frequency of cooperator phenotypes in yeast populations increases dramatically as compared with isolated yeast populations. Bacterial competition stabilizes cooperation within yeast by limiting the yeast population density and also by depleting the public goods produced by cooperating...

  5. Tuning ultrafast electron thermalization pathways in a van der Waals heterostructure

    Massicotte, Mathieu; Watanabe, Kenji; Taniguchi, Takashi; Kong, Jing; Jarillo-Herrero, Pablo; Ma, Qiong; Andersen, Trond Ikdahl; Nair, Nityan L.; Gabor, Nathaniel M.; Lui, Chun Hung; Young, Andrea; Fang, Wenjing; Gedik, Nuh; Koppens, Frank Henricus Louis
    Ultrafast electron thermalization—the process leading to carrier multiplication via impact ionization and hot-carrier luminescence —occurs when optically excited electrons in a material undergo rapid electron–electron scattering to redistribute excess energy and reach electronic thermal equilibrium. Owing to extremely short time and length scales, the measurement and manipulation of electron thermalization in nanoscale devices remains challenging even with the most advanced ultrafast laser techniques. Here, we overcome this challenge by leveraging the atomic thinness of two-dimensional van der Waals (vdW) materials to introduce a highly tunable electron transfer pathway that directly competes with electron thermalization. We realize this scheme in a...

  6. Weyl points in photonic-crystal superlattices

    Bravo-Abad, Jorge; Buljan, Hrvoje; Lu, Ling; Fu, Liang; Soljacic, Marin
    We show that Weyl points can be realized in all-dielectric superlattices based on three-dimensional (3D) layered photonic crystals. Our approach is based on creating an inversion-breaking array of weakly-coupled planar defects embedded in a periodic layered structure with a large omnidirectional photonic band gap. Using detailed band structure calculations and tight-binding theory arguments, we demonstrate that this class of layered systems can be tailored to display 3D linear point degeneracies between two photonic bands, without breaking time-reversal symmetry and using a configuration that is readily-accessible experimentally. These results open new prospects for the observation of Weyl points in the near-infrared...

  7. Enhanced tidal stripping of satellites in the galactic halo from dark matter self-interactions

    Peter, Annika H. G.; Zavala, Jesús; Dooley, Gregory Alan; Frebel, Anna L.; Vogelsberger, Mark
    We investigate the effects of self-interacting dark matter (SIDM) on the tidal stripping and evaporation of satellite galaxies in a Milky Way-like host. We use a suite of five zoom-in, dark-matter-only simulations, two with velocity-independent SIDM cross-sections, two with velocity-dependent SIDM cross-sections, and one cold dark matter (CDM) simulation for comparison. After carefully assigning stellar mass to satellites at infall, we find that stars are stripped at a higher rate in SIDM than in CDM. In contrast, the total bound dark matter mass-loss rate is minimally affected, with subhalo evaporation having negligible effects on satellites for viable SIDM models. Centrally...

  8. Modeling and experiment of the suspended seismometer concept for attenuating the contribution of tilt motion in horizontal measurements

    Evans, M.; Dooley, K. L.; Sohier, H.; Lauriero, A.; Paris, H.; Koch, J.; Knothe, P.; Carbajo, A.; Dufort, C.; Matichard, Fabrice; MacInnis, Myron E; Mittleman, Richard K; Biscans, Sebastien
    Tilt-horizontal coupling in inertial sensors limits the performance of active isolation systems such as those used in gravitational wave detectors. Inertial rotation sensors can be used to subtract the tilt component from the signal produced by horizontal inertial sensors, but such techniques are often limited by the sensor noise of the tilt measurement. A different approach is to mechanically filter the tilt transmitted to the horizontal inertial sensor, as discussed in this article. This technique does not require an auxiliary rotation sensor and can produce a lower noise measurement. The concept investigated uses a mechanical suspension to isolate the inertial...

  9. Seismic isolation of Advanced LIGO: Review of strategy, instrumentation and performance

    Matichard, Fabrice; Mittleman, Richard K; Mason, Kenneth R; Barnum, Sam; Biscans, Sebastien; Evans, Matthew J; Foley, Stephany; Fritschel, Peter K; Hillard, Michael W.; MacInnis, Myron E; Ottaway, David J; Ruet, Laurent; Sarin, Pradeep S; Shoemaker, David H; Stein, Andrew J
    The new generation of gravitational waves detectors require unprecedented levels of isolation from seismic noise. This article reviews the seismic isolation strategy and instrumentation developed for the Advanced LIGO observatories. It summarizes over a decade of research on active inertial isolation and shows the performance recently achieved at the Advanced LIGO observatories. The paper emphasizes the scientific and technical challenges of this endeavor and how they have been addressed. An overview of the isolation strategy is given. It combines multiple layers of passive and active inertial isolation to provide suitable rejection of seismic noise at all frequencies. A detailed presentation...

  10. Anode-coupled readout for light collection in Liquid Argon TPCs

    Moss, Z.; Collin, G.H.; Conrad, J.M.; Toups, Matthew; Bugel, Leonard G.
    This paper will discuss a new method of signal read-out from photon detectors in ultra-large, underground liquid argon time projection chambers. In this design, the signal from the light collection system is coupled via capacitive plates to the TPC wire-planes. This signal is then read out using the same cabling and electronics as the charge information. This greatly benefits light collection: it eliminates the need for an independent readout, substantially reducing cost; it reduces the number of cables in the vapor region of the TPC that can produce impurities; and it cuts down on the number of feed-throughs in the...

  11. Probing the effects of a thermonuclear X-ray burst on the neutron star accretion flow with NuSTAR

    Degenaar, N.; Koljonen, K. I. I.; Kara, E.; Altamirano, D.; Miller, J. M.; Fabian, A. C.; Chakrabarty, Deepto
    Observational evidence has been accumulating that thermonuclear X-ray bursts ignited on the surface of neutron stars influence the surrounding accretion flow. Here, we exploit the excellent sensitivity of NuSTAR up to 79 keV to analyse the impact of an X-ray burst on the accretion emission of the neutron star LMXB 4U 1608−52. The ≃200 s long X-ray burst occurred during a hard X-ray spectral state, and had a peak intensity of ≃30–50 per cent of the Eddington limit with no signs of photospheric radius expansion. Spectral analysis suggests that the accretion emission was enhanced up to a factor of ≃5...

  12. Optical Modulation in the X-Ray Binary 4U 1543–624 Revisited

    Wang, Z.; Tziamtzis, A.; Kaplan, D. L.; Chakrabarty, Deepto
    The X-ray binary 4U 1543–624 has been provisionally identified as an ultra-compact system with an orbital period of ≃ 18 min. We have carried out time-resolved optical imaging of the binary to verify the ultra-short orbital period. Using 140 min of high-cadence r′-band photometry, we recover the previously-seen sinusoidal modulation and determine a period P = 18.20 ± 0.09 min. In addition, we also see a 7.0 × 10⁻⁴ mag min⁻¹ linear decay, likely related to variations in the source's accretion activity. Assuming that the sinusoidal modulation arises from X-ray heating of the inner face of the companion star, we...

  13. Predicting fracture energies and crack-tip fields of soft tough materials

    Zhang, Teng; Lin, Shaoting; Yuk, Hyunwoo; Zhao, Xuanhe
    Soft materials including elastomers and gels are pervasive in biological systems and technological applications. Whereas it is known that intrinsic fracture energies of soft materials are relatively low, how the intrinsic fracture energy cooperates with mechanical dissipation in process zone to give high fracture toughness of soft materials is not well understood. In addition, it is still challenging to predict fracture energies and crack-tip strain fields of soft tough materials. Here, we report a scaling theory that accounts for synergistic effects of intrinsic fracture energies and dissipation on the toughening of soft materials. We then develop a coupled cohesive-zone and...

  14. Matrix elasticity of void-forming hydrogels controls transplanted-stem-cell-mediated bone formation

    Lippens, Evi; Lee, Kangwon; Mehta, Manav; Koshy, Sandeep T.; Darnell, Max C.; Desai, Rajiv M.; Madl, Christopher M.; Xu, Maria; Zhao, Xuanhe; Chaudhuri, Ovijit; Verbeke, Catia; Kim, Woo Seob; Alim, Karen; Mammoto, Akiko; Ingber, Donald E.; Duda, Georg N.; Mooney, David J.; Huebsch, Nathaniel David
    The effectiveness of stem cell therapies has been hampered by cell death and limited control over fate. These problems can be partially circumvented by using macroporous biomaterials that improve the survival of transplanted stem cells and provide molecular cues to direct cell phenotype. Stem cell behaviour can also be controlled in vitro by manipulating the elasticity of both porous and non-porous materials, yet translation to therapeutic processes in vivo remains elusive. Here, by developing injectable, void-forming hydrogels that decouple pore formation from elasticity, we show that mesenchymal stem cell (MSC) osteogenesis in vitro, and cell deployment in vitro and in...

  15. Confirmation of the topology of the Wendelstein 7-X magnetic field to better than 1:100,000

    Maisano-Brown, Jeannette D.
    Fusion energy research has in the past 40 years focused primarily on the tokamak concept, but recent advances in plasma theory and computational power have led to renewed interest in stellarators. The largest and most sophisticated stellarator in the world, Wendelstein 7-X (W7-X), has just started operation, with the aim to show that the earlier weaknesses of this concept have been addressed successfully, and that the intrinsic advantages of the concept persist, also at plasma parameters approaching those of a future fusion power plant. Here we show the first physics results, obtained before plasma operation: that the carefully tailored topology...

  16. Spatially inhomogeneous electron state deep in the extreme quantum limit of strontium titanate

    Bhattacharya, Anand; Khalsa, Guru; Suslov, Alexey V.; Skinner, Brian J
    When an electronic system is subjected to a sufficiently strong magnetic field that the cyclotron energy is much larger than the Fermi energy, the system enters the extreme quantum limit (EQL) and becomes susceptible to a number of instabilities. Bringing a three-dimensional electronic system deeply into the EQL can be difficult however, since it requires a small Fermi energy, large magnetic field, and low disorder. Here we present an experimental study of the EQL in lightly-doped single crystals of strontium titanate. Our experiments probe deeply into the regime where theory has long predicted an interaction-driven charge density wave or Wigner...

  17. RNF166 Determines Recruitment of Adaptor Proteins during Antibacterial Autophagy

    Heath, Robert J.; Goel, Gautam; Baxt, Leigh A.; Rush, Jason S.; Mohanan, Vishnu; Paulus, Geraldine L.C.; Jani, Vijay; Lassen, Kara G.; Xavier, Ramnik Joseph
    Xenophagy is a form of selective autophagy that involves the targeting and elimination of intracellular pathogens through several recognition, recruitment, and ubiquitination events. E3 ubiquitin ligases control substrate selectivity in the ubiquitination cascade; however, systematic approaches to map the role of E3 ligases in antibacterial autophagy have been lacking. We screened more than 600 putative human E3 ligases, identifying E3 ligases that are required for adaptor protein recruitment and LC3-bacteria colocalization, critical steps in antibacterial autophagy. An unbiased informatics approach pinpointed RNF166 as a key gene that interacts with the autophagy network and controls the recruitment of ubiquitin as well...

  18. THE MISSION ACCESSIBLE NEAR-EARTH OBJECTS SURVEY (MANOS): FIRST PHOTOMETRIC RESULTS

    Thirouin, A.; Moskovitz, N.; Christensen, E.; Polishook, D.; Thomas, C. A.; Trilling, D.; Willman, M.; Hinkle, M.; Burt, B.; Avner, D.; Aceituno, F. J.; Binzel, Richard P; DeMeo, Francesca E; Person, Michael J
    The Mission Accessible Near-Earth Objects Survey aims to physically characterize sub-km near-Earth objects (NEOs). We report the first photometric results from the survey that began in 2013 August. Photometric observations were performed using 1–4 m class telescopes around the world. We present rotational periods and light curve amplitudes for 86 sub-km NEOs, though in some cases only lower limits are provided. Our main goal is to obtain light curves for small NEOs (typically, sub-km objects) and estimate their rotational periods, light curve amplitudes, and shapes. These properties are used for a statistical study to constrain overall properties of the NEO...

  19. Experimental testing of a semi-autonomous multi-vehicle collision avoidance algorithm at an intersection testbed

    Rizzi, Andrea; Colombo, Alessandro; Ahn, Heejin; Del Vecchio, Domitilla
    This paper describes the implementation of a multi-vehicle supervisor to prevent collisions at intersections. The experiments are performed on an intersection testbed consisting of three RC cars. Here, we account for uncertainty in car dynamics and state measurement, and the presence of an uncontrolled car, which is human-driven. The supervisor overrides the controlled cars only when necessary to avoid a possible future collision. From the experiments, we demonstrate that intersection collisions are averted, that is, the cars continuously and safely run on the paths without stopping 92.8% of the times.

  20. Design of Driver-Assist Systems Under Probabilistic Safety Specifications Near Stop Signs

    McNew, John M.; Forghani Oozroody, Mojtaba; Hoehener, Daniel Andreas; Del Vecchio, Domitilla
    In this paper, we consider the problem of designing in-vehicle driver-assist systems that warn or override the driver to prevent collisions with a guaranteed probability. The probabilistic nature of the problem naturally arises from many sources of uncertainty, among which the behavior of the surrounding vehicles and the response of the driver to on-board warnings. We formulate this problem as a control problem for uncertain systems under probabilistic safety specifications and leverage the structure of the application domain to reach computationally efficient implementations. Simulations using a naturalistic data set show that the empirical probability of safety is always within 5%...

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