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DASH is a central, open-access repository of research by members of the Harvard community
FAS Scholarly Articles
DASH is a central, open-access repository of research by members of the Harvard community
FAS Scholarly Articles
Shelemay, Kay K.
African and African American Studies
Nevkov, Matey; Liu, Jun; Cai, Tianxi
It is known that for a certain class of single index models (SIMs) zˇSc0, support recovery is impossible when X ~ (0, p×p) and a model complexity adjusted sample size is below a critical threshold. Recently, optimal algorithms based on Sliced Inverse Regression (SIR) were suggested. These algorithms work provably under the assumption that the design X comes from an i.i.d. Gaussian distribution. In the present paper we analyze algorithms based on covariance screening and least squares with L1 penalization (i.e. LASSO) and demonstrate that they can also enjoy optimal (up to a scalar) rescaled sample size in terms of...
Nevkov, Matey; Liu, Jun; Cai, Tianxi
It is known that for a certain class of single index models (SIMs) zˇSc0, support recovery is impossible when X ~ (0, p×p) and a model complexity adjusted sample size is below a critical threshold. Recently, optimal algorithms based on Sliced Inverse Regression (SIR) were suggested. These algorithms work provably under the assumption that the design X comes from an i.i.d. Gaussian distribution. In the present paper we analyze algorithms based on covariance screening and least squares with L1 penalization (i.e. LASSO) and demonstrate that they can also enjoy optimal (up to a scalar) rescaled sample size in terms of...
Burt, Stephen Louis
English and American Literature and Language
Burt, Stephen Louis
English and American Literature and Language
Fu, Wenbo; Gaiotto, Davide; Maldacena, Juan; Sachdev, Subir
We discuss a supersymmetric generalization of the Sachdev-Ye-Kitaev model. These are quantum mechanical models involving N Majorana fermions. The supercharge is given by a polynomial expression in terms of the Majorana fermions with random coefficients. The Hamiltonian is the square of the supercharge. The =1 model with a single supercharge has unbroken supersymmetry at large N, but non-perturbatively spontaneously broken supersymmetry in the exact theory. We analyze the model by looking at the large N equation, and also by performing numerical computations for small values of N. We also compute the large N spectrum of "singlet" operators, where we find...
Fu, Wenbo; Gaiotto, Davide; Maldacena, Juan; Sachdev, Subir
We discuss a supersymmetric generalization of the Sachdev-Ye-Kitaev model. These are quantum mechanical models involving N Majorana fermions. The supercharge is given by a polynomial expression in terms of the Majorana fermions with random coefficients. The Hamiltonian is the square of the supercharge. The =1 model with a single supercharge has unbroken supersymmetry at large N, but non-perturbatively spontaneously broken supersymmetry in the exact theory. We analyze the model by looking at the large N equation, and also by performing numerical computations for small values of N. We also compute the large N spectrum of "singlet" operators, where we find...
Tay, Pei Kun Richie Richie; Nguyen, Peter Q; Joshi, Neel S.
Synthetic biology approaches to bioremediation are a key sustainable strategy to leverage the self-replicating and programmable aspects of biology for environmental stewardship. The increasing spread of anthropogenic mercury pollution into our habitats and food chains is a pressing concern. Here, we explore the use of programmed bacterial biofilms to aid in the sequestration of mercury. We demonstrate that by integrating a mercury-responsive promoter and an operon encoding a mercury-absorbing self-assembling extracellular protein nanofiber, we can engineer bacteria that can detect and sequester toxic Hg2+ ions from the environment. This work paves the way for the development of on-demand biofilm living...
Tay, Pei Kun Richie Richie; Nguyen, Peter Q; Joshi, Neel S.
Synthetic biology approaches to bioremediation are a key sustainable strategy to leverage the self-replicating and programmable aspects of biology for environmental stewardship. The increasing spread of anthropogenic mercury pollution into our habitats and food chains is a pressing concern. Here, we explore the use of programmed bacterial biofilms to aid in the sequestration of mercury. We demonstrate that by integrating a mercury-responsive promoter and an operon encoding a mercury-absorbing self-assembling extracellular protein nanofiber, we can engineer bacteria that can detect and sequester toxic Hg2+ ions from the environment. This work paves the way for the development of on-demand biofilm living...
Moore, Scott; Chong, Stephen N
Hybrid information-flow monitors use a combination of static analysis and dynamic mechanisms to provide precise strong information security guarantees. However, unlike purely static mechanisms for information security, hybrid information-flow monitors incur run-time overhead. We show how static analyses can be used to make hybrid information-flow monitors more efficient, in two ways. First, a simple static analysis can determine when it is sound for a monitor to stop tracking the security level of certain variables. This potentially reduces run-time overhead of the monitor, particularly in applications where sensitive (i.e., confidential or untrusted) data is infrequently introduced to the system. Second, we...
Moore, Scott; Chong, Stephen N
Hybrid information-flow monitors use a combination of static analysis and dynamic mechanisms to provide precise strong information security guarantees. However, unlike purely static mechanisms for information security, hybrid information-flow monitors incur run-time overhead. We show how static analyses can be used to make hybrid information-flow monitors more efficient, in two ways. First, a simple static analysis can determine when it is sound for a monitor to stop tracking the security level of certain variables. This potentially reduces run-time overhead of the monitor, particularly in applications where sensitive (i.e., confidential or untrusted) data is infrequently introduced to the system. Second, we...
Polinsky, Maria; Willis, Oksana
This article examines the knowledge of topic and subject particles in heritage speakers and L2 learners of Japanese and Korean. We assume that topic marking is mediated at the syntaxinformation structure interface, while subject marking pertains to narrow syntax. In comparing phenomena mediated at different levels of linguistic organization, we provide evidence for the hypothesis that information structure-level phenomena present greater challenges for bilingual speakers than those mediated within syntax. While these results may be interpreted as evidence of generalized interface-related deficits, we show that such a global explanation is not supported. Instead, a more nuanced account is developed, based...
Polinsky, Maria; Willis, Oksana
This article examines the knowledge of topic and subject particles in heritage speakers and L2 learners of Japanese and Korean. We assume that topic marking is mediated at the syntaxinformation structure interface, while subject marking pertains to narrow syntax. In comparing phenomena mediated at different levels of linguistic organization, we provide evidence for the hypothesis that information structure-level phenomena present greater challenges for bilingual speakers than those mediated within syntax. While these results may be interpreted as evidence of generalized interface-related deficits, we show that such a global explanation is not supported. Instead, a more nuanced account is developed, based...
Herzfeld, Michael F
Drawing primarily on fieldwork in Greece, Italy, and Thailand, I examine the use of historic conservation to justify gentrification. This commoditization of history expands into urban design a classification that serves the goals of neoliberal modernity. By thus refocusing the classic anthropological concern with taxonomy on the analysis of the bureaucratic production of everyday experience and knowledge, I explore a new global habitus in which dominant interpretations of history spatially reinforce current ideologies. Historic conservation often provides an excuse for intervention into urban life. In a revision of high modernism’s focus on science, logic, and efficiency, this trend invokes “the...
Roth, Paul; Buchowski, Michal; Clifford, James; Herzfeld, Michael F; Sangren, P.; Sapire, David; Strathern, Marilyn; Tyler, Stephen
Anthropology
Sijacki, Debora; Vogelsberger, Mark; Kere?, Du?an; Springel, Volker; Hernquist, Lars Eric
We present a detailed comparison between the well-known smoothed particle hydrodynamics (SPH) code gadget and the new moving-mesh code arepo on a number of hydrodynamical test problems. Through a variety of numerical experiments with increasing complexity we establish a clear link between simple test problems with known analytic solutions and systematic numerical effects seen in cosmological simulations of galaxy formation. Our tests demonstrate deficiencies of the SPH method in several sectors. These accuracy problems not only manifest themselves in idealized hydrodynamical tests, but also propagate to more realistic simulation set-ups of galaxy formation, ultimately affecting local and global gas properties...
Hayward, Christopher C.; Jonsson, Patrik; Kere?, Du?an; Magnelli, Benjamin; Hernquist, Lars Eric; Cox, T. J.
In recent work, we have suggested that the high-redshift (z∼ 2–4) bright submillimetre galaxy (SMG) population is heterogeneous, with major mergers contributing both at early stages, where quiescently star-forming discs are blended into one submm source (‘galaxy-pair SMGs’), and at late stages, where mutual tidal torques drive gas inflows and cause strong starbursts. Here we combine hydrodynamic simulations of major mergers with 3D dust radiative transfer calculations to determine observational diagnostics that can distinguish between quiescently star-forming SMGs and starburst SMGs via integrated data alone. We fit the far-infrared (FIR) spectral energy distributions of the simulated galaxies with the optically...
Snyder, Gregory; Hayward, Christopher C.; Sajina, Anna; Jonsson, Patrik; Cox, Thomas J.; Hernquist, Lars Eric; Hopkins, Philip F.; Yan, Lin
We analyze the link between active galactic nuclei (AGNs) and mid-infrared flux using dust radiative transfer calculations of starbursts realized in hydrodynamical simulations. Focusing on the effects of galaxy dust, we evaluate diagnostics commonly used to disentangle AGN and star formation in ultraluminous infrared galaxies (ULIRGs). We examine these quantities as a function of time, viewing angle, dust model, AGN spectrum, and AGN strength in merger simulations representing two possible extremes of the ULIRG population: one is a typical gas-rich merger at z ~ 0, and the other is characteristic of extremely obscured starbursts at z ~ 2-4. This highly...
Herman, Michael J.; Kuang, Zhiming
[1] Two 1-D atmospheric column models containing convective parameterization schemes are compared to a 3-D cloud system resolving model (CSRM) using a recent technique that admits study of responses of convection to small temperature and moisture anomalies. The MIT Single-Column Model (MSCM) and Diabat3 (D3) are the column models of study. There exist notable differences between the responses of the column models and those of the CSRM. Both column models retain prescribed temperature anomalies and MSCM retains moisture anomalies for much longer than the CSRM. D3 excessively warms anomalous moist layers. Neither column model warms the upper troposphere following moist...
Hayward, C. C.; Narayanan, D.; Keres, D.; Jonsson, P.; Hopkins, P. F.; Cox, T. J.; Hernquist, Lars Eric
High-redshift submillimetre galaxies (SMGs) are some of the most rapidly star-forming galaxies in the Universe. Historically, galaxy formation models have had difficulty explaining the observed number counts of SMGs. We combine a semi-empirical model with 3D hydrodynamical simulations and 3D dust radiative transfer to predict the number counts of unlensed SMGs. Because the stellar mass functions, gas and dust masses, and sizes of our galaxies are constrained to match observations, we can isolate uncertainties related to the dynamical evolution of galaxy mergers and the dust radiative transfer. The number counts and redshift distributions predicted by our model agree well with...