Últimos itens adicionados do Acervo: Harvard University

A Universidade de Harvard (em inglês: Harvard University) é uma universidade privada membro da Ivy League, localizada em Cambridge, Massachusetts, Estados Unidos, e cuja história, influência e riqueza tornam-a uma das mais prestigiadas universidades do mundo.

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Chemical basis of Trotter-Suzuki errors in quantum chemistry simulation

Babbush, Ryan; McClean, Jarrod Ryan; Wecker, Dave; Aspuru-Guzik, Alan; Wiebe, Nathan
Fonte: American Physical Society (APS) Publicador: American Physical Society (APS)
Tipo: Artigo de Revista Científica
EN_US
Although the simulation of quantum chemistry is one of the most anticipated applications of quantum computing, the scaling of known upper bounds on the complexity of these algorithms is daunting. Prior work has bounded errors due to discretization of the time evolution (known as “Trotterization”) in terms of the norm of the error operator and analyzed scaling with respect to the number of spin orbitals. However, we find that these error bounds can be loose by up to 16 orders of magnitude for some molecules. Furthermore, numerical results for small systems fail to reveal any clear correlation between ground-state error and number of spin orbitals. We instead argue that chemical properties, such as the maximum nuclear charge in a molecule and the filling fraction of orbitals, can be decisive for determining the cost of a quantum simulation. Our analysis motivates several strategies to use classical processing to further reduce the required Trotter step size and estimate the necessary number of steps, without requiring additional quantum resources. Finally, we demonstrate improved methods for state preparation techniques which are asymptotically superior to proposals in the simulation literature.; Chemistry and Chemical Biology

Boson sampling for molecular vibronic spectra

Huh, Joonsuk; Guerreschi, Gian Giacomo; Peropadre, Borja; McClean, Jarrod R.; Aspuru-Guzik, Alan
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
EN_US
Controllable quantum devices open novel directions to both quantum computation and quantum simulation. Recently, a problem known as boson sampling has been shown to provide a pathway for solving a computationally intractable problem without the need for a full quantum computer, instead using a linear optics quantum set-up. In this work, we propose a modification of boson sampling for the purpose of quantum simulation. In particular, we show that, by means of squeezed states of light coupled to a boson sampling optical network, one can generate molecular vibronic spectra, a problem for which no efficient classical algorithm is currently known. We provide a general framework for carrying out these simulations via unitary quantum optical transformations and supply specific molecular examples for future experimental realization.; Chemistry and Chemical Biology

Quantum Simulation of Helium Hydride Cation in a Solid-State Spin Register

Wang, Ya; Dolde, Florian; Biamonte, Jacob; Babbush, Ryan; Bergholm, Ville; Yang, Sen; Jakobi, Ingmar; Neumann, Philipp; Aspuru-Guzik, Alan; Whitfield, James D.; Wrachtrup, Jörg
Fonte: American Chemical Society (ACS) Publicador: American Chemical Society (ACS)
Tipo: Artigo de Revista Científica
EN_US
b initio computation of molecular properties is one of the most promising applications of quantum computing. While this problem is widely believed to be intractable for classical computers, efficient quantum algorithms exist which have the potential to vastly accelerate research throughput in fields ranging from material science to drug discovery. Using a solid-state quantum register realized in a nitrogen-vacancy (NV) defect in diamond, we compute the bond dissociation curve of the minimal basis helium hydride cation, HeH+. Moreover, we report an energy uncertainty (given our model basis) of the order of 10–14 hartree, which is 10 orders of magnitude below the desired chemical precision. As NV centers in diamond provide a robust and straightforward platform for quantum information processing, our work provides an important step toward a fully scalable solid-state implementation of a quantum chemistry simulator.; Chemistry and Chemical Biology

Quantum process tomography by 2D fluorescence spectroscopy

Pachón, Leonardo A.; Marcus, Andrew H.; Aspuru-Guzik, Alan
Fonte: AIP Publishing Publicador: AIP Publishing
Tipo: Artigo de Revista Científica
EN_US
Reconstruction of the dynamics (quantum process tomography) of the single-exciton manifold in energy transfer systems is proposed here on the basis of two-dimensional fluorescence spectroscopy (2D-FS) with phase-modulation. The quantum-process-tomography protocol introduced here benefits from, e.g., the sensitivity enhancement ascribed to 2D-FS. Although the isotropically averaged spectroscopic signals depend on the quantum yield parameter Γ of the doubly excited-exciton manifold, it is shown that the reconstruction of the dynamics is insensitive to this parameter. Applications to foundational and applied problems, as well as further extensions, are discussed.; Chemistry and Chemical Biology

Compressed Sensing for the Fast Computation of Matrices: Application to Molecular Vibrations

Sanders, Jacob Nathan; Andrade, Xavier; Aspuru-Guzik, Alan
Fonte: American Chemical Society (ACS) Publicador: American Chemical Society (ACS)
Tipo: Artigo de Revista Científica
EN_US
This article presents a new method to compute matrices from numerical simulations based on the ideas of sparse sampling and compressed sensing. The method is useful for problems where the determination of the entries of a matrix constitutes the computational bottleneck. We apply this new method to an important problem in computational chemistry: the determination of molecular vibrations from electronic structure calculations, where our results show that the overall scaling of the procedure can be improved in some cases. Moreover, our method provides a general framework for bootstrapping cheap low-accuracy calculations in order to reduce the required number of expensive high-accuracy calculations, resulting in a significant 3⇥ speed-up in actual calculations.; Chemistry and Chemical Biology

"Utopian socialism and social science"

Picon, Antoine
Fonte: Harvard University Publicador: Harvard University
Tipo: Outros
EN_US

A Proposed Map of a Geodesign Research Agenda: Eleven Key Questions in an Eight-pole Space

Ervin, Stephen M.
Fonte: Wichmann-Verlag Publicador: Wichmann-Verlag
Tipo: Conference Paper
EN_US
The development of a robust and credible geodesign discipline will depend equally upon an ever-growing inventory of excellent real-world examples of projects embodying geodesign principles, and upon the development and pursuit of a rich and rigorous research agenda that informs geodesign theory and practice. To this end, following a consideration of several precedents from the GIS literature, a research space with eight poles is proposed. Mapping twenty or so not-quite-randomly collected examples of proposed research ques­tions into this space yields a promising framework for an emergent research agenda, summarized by eleven key geodesign research questions.

Allergic Lung Inflammation Aggravates Angiotensin II–Induced Abdominal Aortic Aneurysms in Mice

Liu, Cong-Lin; Wang, Yi; Liao, Mengyang; Wemmelund, Holger; Ren, Jingyuan; Fernandes, Cleverson; Zhou, Yi; Sukhova, Galina K.; Lindholt, Jes S.; Johnsen, Søren P.; Zhang, Jin-Ying; Cheng, Xiang; Huang, Xiaozhu; Daugherty, Alan; Levy, Bruce David; Libby,
Fonte: Ovid Technologies (Wolters Kluwer Health) Publicador: Ovid Technologies (Wolters Kluwer Health)
Tipo: Artigo de Revista Científica
EN_US

Targeting Interleukin-1β Reduces Leukocyte Production After Acute Myocardial Infarction

Sager, Hendrik B.; Heidt, Timo; Hulsmans, Maarten; Dutta, Partha; Courties, Gabriel P; Sebas, Matthew; Wojtkiewicz, Gregory R.; Tricot, Benoit; Iwamoto, Yoshiko; Sun, Yuan; Weissleder, Ralph; Libby, Peter; Swirski, Filip K.; Nahrendorf, Matthias
Fonte: Ovid Technologies (Wolters Kluwer Health) Publicador: Ovid Technologies (Wolters Kluwer Health)
Tipo: Artigo de Revista Científica
EN_US
Background—Myocardial infarction (MI) is an ischemic wound that recruits millions of leukocytes. MI-associated blood leukocytosis correlates inversely with patient survival, yet the signals driving heightened leukocyte production after MI remain incompletely understood. Methods and Results—With the use of parabiosis surgery, this study shows that soluble danger signals, among them interleukin-1β, increase bone marrow hematopoietic stem cell proliferation after MI. Data obtained in bone marrow reconstitution experiments reveal that interleukin-1β enhances hematopoietic stem cell proliferation by both direct actions on hematopoietic cells and through modulation of the bone marrow’s hematopoietic microenvironment. An antibody that neutralizes interleukin-1β suppresses these effects. Anti-interleukin-1β treatment dampens the post-MI increase in hematopoietic stem cell proliferation. Consequently, decreased leukocyte numbers in the blood and infarct reduce inflammation and diminish post-MI heart failure in ApoE–/– mice with atherosclerosis. Conclusions—The presented insight into post-MI bone marrow activation identifies a mechanistic target for muting inflammation in the ischemically damaged heart.

Lp-PLA 2 Antagonizes Left Ventricular Healing After Myocardial Infarction by Impairing the Appearance of Reparative MacrophagesCLINICAL PERSPECTIVE

He, Shun; Chousterman, Benjamin; Fenn, Ashley Margaret; Anzai, Atsushi; Nairz, Manfred; Brandt, Martin; Hilgendorf, Ingo; Sun, Yuan; Ye, Yu-Xiang; Iwamoto, Yoshiko; Tricot, Benoit; Weissleder, Ralph; Macphee, Colin; Libby, Peter; Nahrendorf, Matthias; Swi
Fonte: Ovid Technologies (Wolters Kluwer Health) Publicador: Ovid Technologies (Wolters Kluwer Health)
Tipo: Artigo de Revista Científica
EN_US
Background—Healing after myocardial infarction (MI) involves the biphasic accumulation of inflammatory Ly-6Chigh and reparative Ly-6Clow monocytes/macrophages. Excessive inflammation disrupts the balance between the 2 phases, impairs infarct healing, and contributes to left ventricle remodeling and heart failure. Lipoprotein-associated phospholipase A2 (Lp-PLA2), a member of the phospholipase A2 family of enzymes, produced predominantly by leukocytes, participates in host defenses and disease. Elevated Lp-PLA2 levels associate with increased risk of cardiovascular events across diverse patient populations, but the mechanisms by which the enzyme elicits its effects remain unclear. This study tested the role of Lp-PLA2 in healing after MI. Methods and Results—In response to MI, Lp-PLA2 levels markedly increased in the circulation. To test the functional importance of Lp-PLA2, we generated chimeric mice whose bone marrow–derived leukocytes were Lp-PLA2–deficient (bmLp-PLA2−/−). Compared with wild-type controls, bmLp-PLA2−/− mice subjected to MI had lower serum levels of inflammatory cytokines tumor necrosis factor-α, interleukin (IL)-1β, and IL-6, and decreased number of circulating inflammatory myeloid cells. Accordingly...

Adequacy of Outpatient Specialty Care Access in Marketplace Plans Under the Affordable Care Act

Dorner, Stephen Christopher; Jacobs, Douglas Bernard; Sommers, Benjamin Daniel
Fonte: American Medical Association (AMA) Publicador: American Medical Association (AMA)
Tipo: Artigo de Revista Científica
EN_US

The Paradox of Self-Amendment: A Study of Law, Logic, Omnipotence, and Change

Suber, Peter
Fonte: Peter Lang International Academic Publishers. Publicador: Peter Lang International Academic Publishers.
Tipo: Monograph or Book
EN_US
The first full-length study of self-reference and paradox in law, this book will intrigue and instruct anyone interested in law, logic, philosophy, or political theory. History shows that self-amendment - for example, the use of a constitution's amending clause to amend itself - is commonplace; legal analysis shows it to be lawful, even if (as some logicians have alleged) it is self-contradictory; and philosophical analysis shows it to be foundational for legality. The lawfulness of self-amendment, therefore, sheds important light on legal reasoning and rationality, and shows that we no longer need accept the immutability of any level of law.

Public Policy, Price Shocks, and Civil War in Developing Countries

Bates, Robert H.
Fonte: Harvard University Publicador: Harvard University
Tipo: Research Paper or Report
EN_US
Those who study the role of agriculture in the political economy of development focus on government policy choices on the one hand and the impact of price shocks on the other. We argue that the two should be studied together. We find that civil unrest (Granger) causes government policies, pushing governments in poor and medium income countries to shift relative prices in favor of urban consumers. We also find that while civil wars are related to food price shocks, when government policy choices are taken into account, the relationship disappears. We thus learn two things: Policies that placate urban consumers may inflict economic costs on governments, but they confer political benefits. And when estimating the relationship between price shocks and political stability, equations that omit the policy response of governments are misspecified.; Government

Public Policy, Price Shocks, and Conflict: Price Shocks and Civil War in Developing Countries

Bates, Robert H.; Carter, Brett
Fonte: Harvard University Publicador: Harvard University
Tipo: Research Paper or Report
EN_US
Those who study the role of agriculture in the political economy of development focus on government policy choices on the one hand and the impact of price shocks on the other. We argue that the two should be studied together. We find that civil unrest (Granger) causes government policies, pushing governments in poor and medium income countries to shift relative prices in favor of urban consumers. We also find that while civil wars are related to food price shocks, when government policy choices are taken into account, the relationship disappears. We thus learn two things: Policies that placate urban consumers may inflict economic costs on governments, but they confer political benefits. And when estimating the relationship between price shocks and political stability, equations that omit the policy response of governments are misspecified.; Government

Terminal Schwann Cells Participate in Neuromuscular Synapse Remodeling during Reinnervation following Nerve Injury

Kang, Hyuno; Tian, Le; Mikesh, Michelle; Lichtman, Jeff; Thompson, Wesley J.
Fonte: Society for Neuroscience Publicador: Society for Neuroscience
Tipo: Artigo de Revista Científica
EN_US
Schwann cells (SCs) at neuromuscular junctions (NMJs) play active roles in synaptic homeostasis and repair. We have studied how SCs contribute to reinnervation of NMJs using vital imaging of mice whose motor axons and SCs are transgenically labeled with different colors of fluorescent proteins. Motor axons most commonly regenerate to the original synaptic site by following SC-filled endoneurial tubes. During the period of denervation, SCs at the NMJ extend elaborate processes from the junction, as shown previously, but they also retract some processes from territory they previously occupied within the endplate. The degree of this retraction depends on the length of the period of denervation. We show that the topology of the remaining SC processes influences the branching pattern of regenerating axon terminals and the redistribution of acetylcholine receptors (AChRs). Upon arriving at the junction, regenerating axons follow existing SC processes within the old synaptic site. Some of the AChR loss that follows denervation is correlated with failure of portions of the old synaptic site that lack SC coverage to be reinnervated. New AChR clustering is also induced by axon terminals that follow SC processes extended during denervation. These observations show that SCs participate actively in the remodeling of neuromuscular synapses following nerve injury by their guidance of axonal reinnervation.; Molecular and Cellular Biology

Motor Axon Regeneration and Muscle Reinnervation in Young Adult and Aged Animals

Kang, Hyuno; Lichtman, Jeff
Fonte: Society for Neuroscience Publicador: Society for Neuroscience
Tipo: Artigo de Revista Científica
EN_US
Injuries to peripheral nerves can cause paralysis and sensory disturbances, but such functional impairments are often short lived because of efficient regeneration of damaged axons. The time required for functional recovery, however, increases with advancing age (Verdú et al., 2000; Kawabuchi et al., 2011). Incomplete or delayed recovery after peripheral nerve damage is a major health concern in the aging population because it can severely restrict a person's mobility and independence. A variety of possible causes have been suggested to explain why nervous systems in aged individuals recover more slowly from nerve damage. Potential causes include age-related declines in the regenerative potential of peripheral axons and decreases in the supply or responsivity to trophic and/or tropic factors. However, there have been few direct analyses of age-related axon regeneration. Our aim here was to observe axons directly in young and old mice as they regenerate and ultimately reoccupy denervated neuromuscular synaptic sites to learn what changes in this process are age related. We find that damaged nerves in aged animals clear debris more slowly than nerves in young animals and that the greater number of obstructions regenerating axons encounter in the endoneurial tubes of old animals give rise to slower regeneration. Surprisingly...

Attenuation of age-related changes in mouse neuromuscular synapses by caloric restriction and exercise

Valdez, G; Tapia, J; Kang, H.; Clemenson, G. D.; Gage, F. H.; Lichtman, Jeff; Sanes, Joshua R.
Fonte: Proceedings of the National Academy of Sciences Publicador: Proceedings of the National Academy of Sciences
Tipo: Artigo de Revista Científica
EN_US
The cellular basis of age-related behavioral decline remains obscure but alterations in synapses are likely candidates. Accordingly, the beneficial effects on neural function of caloric restriction and exercise, which are among the most effective anti-aging treatments known, might also be mediated by synapses. As a starting point in testing these ideas, we studied the skeletal neuromuscular junction (NMJ), a large, accessible peripheral synapse. Comparison of NMJs in young adult and aged mice revealed a variety of age-related structural alterations, including axonal swellings, sprouting, synaptic detachment, partial or complete withdrawal of axons from some postsynaptic sites, and fragmentation of the postsynaptic specialization. Alterations were significant by 18 mo of age and severe by 24 mo. A life-long calorie-restricted diet significantly decreased the incidence of pre- and postsynaptic abnormalities in 24-mo-old mice and attenuated age-related loss of motor neurons and turnover of muscle fibers. One month of exercise (wheel running) in 22-mo-old mice also reduced age-related synaptic changes but had no effect on motor neuron number or muscle fiber turnover. Time-lapse imaging in vivo revealed that exercise partially reversed synaptic alterations that had already occurred. These results demonstrate a critical effect of aging on synaptic structure and provide evidence that interventions capable of extending health span and lifespan can partially reverse these age-related synaptic changes.; Molecular and Cellular Biology

Functional muscle regeneration with combined delivery of angiogenesis and myogenesis factors

Borselli, C.; Storrie, H.; Benesch-Lee, F.; Shvartsman, Dmitry; Cezar, Christine Anne; Lichtman, Jeff; Vandenburgh, H. H.; Mooney, David J.
Fonte: Proceedings of the National Academy of Sciences Publicador: Proceedings of the National Academy of Sciences
Tipo: Artigo de Revista Científica
EN_US
Regenerative efforts typically focus on the delivery of single factors, but it is likely that multiple factors regulating distinct aspects of the regenerative process (e.g., vascularization and stem cell activation) can be used in parallel to affect regeneration of functional tissues. This possibility was addressed in the context of ischemic muscle injury, which typically leads to necrosis and loss of tissue and function. The role of sustained delivery, via injectable gel, of a combination of VEGF to promote angiogenesis and insulin-like growth factor-1 (IGF1) to directly promote muscle regeneration and the return of muscle function in ischemic rodent hindlimbs was investigated. Sustained VEGF delivery alone led to neoangiogenesis in ischemic limbs, with complete return of tissue perfusion to normal levels by 3 weeks, as well as protection from hypoxia and tissue necrosis, leading to an improvement in muscle contractility. Sustained IGF1 delivery alone was found to enhance muscle fiber regeneration and protected cells from apoptosis. However, the combined delivery of VEGF and IGF1 led to parallel angiogenesis, reinnervation, and myogenesis; as satellite cell activation and proliferation was stimulated, cells were protected from apoptosis...

Lysosomal Activity Associated with Developmental Axon Pruning

Song, J; Misgeld, T.; Kang, H; Knecht, S.; Lu, J; Cao, Y.; Cotman, Susan L.; Bishop, D. L.; Lichtman, Jeff
Fonte: Society for Neuroscience Publicador: Society for Neuroscience
Tipo: Artigo de Revista Científica
EN_US
Clearance of cellular debris is a critical feature of the developing nervous system, as evidenced by the severe neurological consequences of lysosomal storage diseases in children. An important developmental process, which generates considerable cellular debris, is synapse elimination, in which many axonal branches are pruned. The fate of these pruned branches is not known. Here, we investigate the role of lysosomal activity in neurons and glia in the removal of axon branches during early postnatal life. Using a probe for lysosomal activity, we observed robust staining associated with retreating motor axons. Lysosomal function was involved in axon removal because retreating axons were cleared more slowly in a mouse model of a lysosomal storage disease. In addition, we found lysosomal activity in the cerebellum at the time of, and at sites where, climbing fibers are eliminated. We propose that lysosomal activity is a central feature of synapse elimination. Moreover, staining for lysosomal activity may serve as a marker for regions of the developing nervous system undergoing axon pruning.; Molecular and Cellular Biology

Who Makes History? American Religious Historians and the Problem of Historical Agency

Brekus, Catherine A
Fonte: Harvard University Publicador: Harvard University
Tipo: Artigo de Revista Científica
EN_US