48 research outputs found
Exploration of the role of diquarks in hadrons using lattice QCD
Get PDFThesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2006.Includes bibliographical references (p. 76-78).We perform a number of measurements relevant to nuclear and particle physics by using the tools of lattice QCD. We verify our lattice calculations by reproducing published meson masses. We then study the light quark distribution in a meson with one heavy quark. After improving our methods in the meson case, we conclude by looking at the correlation between the two light quarks in a baryon. We find evidence for these quarks binding into spatially extended diquarks.by Patrick S. Varilly.S.B
Communication: a simple analytical formula for the free energy of ligand-receptor-mediated interactions.
No full textRecently [P. Varilly, S. Angioletti-Uberti, B. M. Mognetti, and D. Frenkel, "A general theory of DNA-mediated and other valence-limited colloidal interactions," J. Chem. Phys. 137, 094108 (2012)], we presented a general theory for calculating the strength and properties of colloidal interactions mediated by ligand-receptor bonds (such as those that bind DNA-coated colloids). In this Communication, we derive a surprisingly simple analytical form for the interaction free energy, which was previously obtainable only via a costly numerical thermodynamic integration. As a result, the computational effort to obtain potentials of interaction is significantly reduced. Moreover, we can gain insight from this analytic expression for the free energy in limiting cases. In particular, the connection of our general theory to other previous specialised approaches is now made transparent. This important simplification will significantly broaden the scope of our theory.Journal ArticleResearch Support, Non-U.S. Gov'tResearch Support, U.S. Gov't, Non-P.H.S.info:eu-repo/semantics/publishe
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Fluctuations in Water and their Relation to the Hydrophobic Effect
Get PDFThe hydrophobic effect, or the tendency for oil and water not to mix, is a fundamental force that strongly influences the shape, behavior and assembly of solutes in solution. Hydrophobicity emerges from the collective behavior of large numbers of solvent molecules, so its accurate treatment is challenging. A decade ago, Lum, Chandler and Weeks (LCW) addressed this challenge indirectly by modeling how solvent density fluctuations couple to external solutes and constraints, and then inferring hydrophobic behavior from the resulting mean solvent density. LCW theory is successful because it distinguishes between, and separately models, small-length-scale and large-length-scale density fluctuations. In this thesis, we develop methods for probing the statistics of large-length-scale density fluctuations in computer simulations of water. We use these tools to study solvation phenomena in model systems and in proteins, in bulk water and near surfaces, and we rationalize these phenomena in terms of LCW ideas. Building on these ideas and on past efforts by others, we construct a tractable, efficient and accurate theory of solvation on a coarse-grained lattice. The final theory allows us to model the solvation behavior of uncharged, static solutes of arbitrary shape, and we outline the steps necessary to model charged, dynamic solutes in the future. A unifying thread in our solvation studies is the importance of fluctuations of liquid-vapor interfaces. At the end of this thesis, we describe how these fluctuations may play a role in water evaporation
Transcendental obstructions to weak approximation on general K3 surfaces
No full textAbstractWe construct an explicit K3 surface over the field of rational numbers that has geometric Picard rank one, and for which there is a transcendental Brauer–Manin obstruction to weak approximation. To do so, we exploit the relationship between polarized K3 surfaces endowed with particular kinds of Brauer classes and cubic fourfolds
Water Evaporation: A Transition Path Sampling Study
No full textWe use transition path sampling to study evaporation
in the SPC/E
model of liquid water. On the basis of thousands of evaporation trajectories,
we characterize the members of the transition state ensemble (TSE),
which exhibit a liquid–vapor interface with predominantly negative
mean curvature at the site of evaporation. We also find that after
evaporation is complete, the distributions of translational and angular
momenta of the evaporated water are Maxwellian with a temperature
equal to that of the liquid. To characterize the evaporation trajectories
in their entirety, we find that it suffices to project them onto just
two coordinates: the distance of the evaporating molecule to the instantaneous
liquid–vapor interface and the velocity of the water along
the average interface normal. In this projected space, we find that
the TSE is well-captured by a simple model of ballistic escape from
a deep potential well, with no additional barrier to evaporation beyond
the cohesive strength of the liquid. Equivalently, they are consistent
with a near-unity probability for a water molecule impinging upon
a liquid droplet to condense. These results agree with previous simulations
and with some, but not all, recent experiments
A general theory of DNA-mediated and other valence-limited colloidal interactions.
No full textWe present a general theory for predicting the interaction potentials between DNA-coated colloids, and more broadly, any particles that interact via valence-limited ligand-receptor binding. Our theory correctly incorporates the configurational and combinatorial entropic factors that play a key role in valence-limited interactions. By rigorously enforcing self-consistency, it achieves near-quantitative accuracy with respect to detailed Monte Carlo calculations. With suitable approximations and in particular geometries, our theory reduces to previous successful treatments, which are now united in a common and extensible framework. We expect our tools to be useful to other researchers investigating ligand-mediated interactions. A complete and well-documented Python implementation is freely available at http://github.com/patvarilly/DNACC.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe
Diquark correlations in a hadron from lattice QCD
No full textUsing lattice QCD, a diquark can be studied in a gauge-invariant manner by binding it to a static quark in a heavylight-light hadron. We compute the simultaneous two-quark density of a diquark, including corrections for periodic boundary conditions. We define a correlation function to isolate the intrinsic correlations of the diquark and reduce the effects caused by the presence of the static quark. Away from the immediate vicinity of the static quark, the diquark has a consistent shape, with much stronger correlations seen in the good (scalar) diquark than in the bad (axial-vector) diquark. We present results for mπ = 293 MeV as well as mπ = 940 MeV, and discuss the behavior as the pion mass changes.United States. Dept. of Energy (Grant DE-FG02-96ER40965)United States. Dept. of Energy (Grant No. DE-FG02- 94ER40818)Massachusetts Institute of Technology. Undergraduate Research Opportunities Progra
