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Publications

Control of propagating spin waves via spin transfer torque in a metallic bilayer waveguide

Cornell Affiliated Author(s)
Author
Kyongmo An
Daniel Birt
Chi-Feng Pai
Kevin Olsson
Daniel Ralph
Robert Buhrman
Xiaoqin Li
Abstract

We investigate the effect of a direct current on propagating spin waves in a CoFeB/Ta bilayer structure. Using the micro-Brillouin light scattering technique, we observe that the spin-wave damping and amplitude may be attenuated or amplified depending on the direction of the current and the applied magnetic field. Our work suggests an effective approach for electrically controlling the propagation of spin waves in a magnetic waveguide and may be useful in a number of applications such as phase-locked nano-oscillators and hybrid information-processing devices.

Journal
American Physical Society (APS)
Date Published
Funding Source
DGE-0549417

Spontaneous emergence of large-scale cell cycle synchronization in amoeba colonies

Cornell Affiliated Author(s)
Author
Igor Segota
Laurent Boulet
David Franck
Carl Franck
Abstract

Unicellular eukaryotic amoebae Dictyostelium discoideum are generally believed to grow in their vegetative state as single cells until starvation, when their collective aspect emerges and they differentiate to form a multicellular slime mold. While major efforts continue to be aimed at their starvation-induced social aspect, our understanding of population dynamics and cell cycle in the vegetative growth phase has remained incomplete. Here we show that cell populations grown on a substrate spontaneously synchronize their cell cycles within several hours.

Journal
Physical Biology
Date Published
Funding Source
DMR-1120296
Group (Lab)
Carl Franck Group

A recipe for free-energy functionals of polarizable molecular fluids

Cornell Affiliated Author(s)
Author
R. Sundararaman
K. Letchworth-Weaver
Tomas Arias
Abstract

Classical density-functional theory is the most direct approach to equilibrium structures and free energies of inhomogeneous liquids, but requires the construction of an approximate free-energy functional for each liquid of interest. We present a general recipe for constructing functionals for small-molecular liquids based only on bulk experimental properties and ab initio calculations of a single solvent molecule.

Journal
Journal of Chemical Physics
Date Published
Funding Source
OCI-1053575
DE-SC0001086
1053575
Group (Lab)
Tomas Arias Group

Mechanical properties of growing melanocytic nevi and the progression to melanoma

Cornell Affiliated Author(s)
Author
A. Taloni
A.A. Alemi
E. Ciusani
J.P. Sethna
S. Zapperi
C.A.M. La Porta
Abstract

Melanocytic nevi are benign proliferations that sometimes turn into malignant melanoma in a way that is still unclear from the biochemical and genetic point of view. Diagnostic and prognostic tools are then mostly based on dermoscopic examination and morphological analysis of histological tissues. To investigate the role of mechanics and geometry in the morpholgical dynamics of melanocytic nevi, we study a computation model for cell proliferation in a layered non-linear elastic tissue.

Journal
PLoS ONE
Date Published
Funding Source
PHY-0941095
PHY-1066293
U54CA143876
Research Area
Group (Lab)
James Sethna Group

Evaluation of mode dependent fluid damping in a high frequency drumhead microresonator

Cornell Affiliated Author(s)
Author
S.D. Vishwakarma
A.K. Pandey
J.M. Parpia
D.R. Southworth
H.G. Craighead
R. Pratap
Abstract

Design of high quality factor (Q) micromechanical resonators depends critically on our understanding of energy losses in their oscillations. The Q of such structures depends on process induced prestress in the structural geometry, interaction with the external environment, and the encapsulation method. We study the dominant fluid interaction related losses, namely, the squeeze film damping and acoustic radiation losses in a drumhead microresonator subjected to different prestress levels, operated in air, to predict its Q in various modes of oscillation.

Journal
Journal of Microelectromechanical Systems
Date Published
Funding Source
1001742
1120296
Group (Lab)
Jeevak Parpia Group

Topological excitations and the dynamic structure factor of spin liquids on the kagome lattice

Cornell Affiliated Author(s)
Author
Matthias Punk
Debanjan Chowdhury
Subir Sachdev
Abstract

Recent neutron scattering experiments on the spin-1/2 kagome lattice antiferromagnet ZnCu 3 (OH) 6 Cl 2 (Herbertsmithite) provide the first evidence of fractionalized excitations in a quantum spin liquid state in two spatial dimensions. In contrast to existing theoretical models of both gapped and gapless spin liquids, which give rise to sharp dispersing features in the dynamic structure factor, the measured dynamic structure factor reveals an excitation continuum that is remarkably flat as a function of frequency.

Journal
Nature Physics
Date Published
Funding Source
3077-N16
DMR-1103860
1103860
Group (Lab)
Debanjan Chowdhury Group

Biaxial shear of confined colloidal hard spheres: The structure and rheology of the vorticity-aligned string phase

Cornell Affiliated Author(s)
Author
N.Y.C. Lin
X. Cheng
Itai Cohen
Abstract

Using a novel biaxial confocal rheoscope, we investigate the flow of the shear induced vorticity aligned string phase [X. Cheng et al., Proc. Natl. Acad. Sci. U. S. A., 2011, 109, 63], which has a highly anisotropic microstructure. Using biaxial shear protocols we show that we have excellent control of the string phase anisotropic morphology. We choose a shear protocol that drives the system into the string phase. Subsequently, a biaxial force measurement device is used to determine the suspension rheology along both the flow and vorticity directions.

Journal
Soft Matter
Date Published
Group (Lab)
Itai Cohen Group

Super-resolution microscopy reveals decondensed chromatin structure at transcription sites

Cornell Affiliated Author(s)
Author
Y. Wang
S. Maharana
M.D. Wang
G.V. Shivashankar
Abstract

Remodeling of the local chromatin structure is essential for the regulation of gene expression. While a number of biochemical and bioimaging experiments suggest decondensed chromatin structures are associated with transcription, a direct visualization of DNA and transcriptionally active RNA polymerase II (RNA pol II) at super-resolution is still lacking. Here we investigate the structure of chromatin isolated from HeLa cells using binding activatable localization microscopy (BALM). The sample preparation method preserved the structural integrity of chromatin.

Journal
Scientific Reports
Date Published
Research Area
Group (Lab)
Michelle Wang Group

Spectroscopic accuracy directly from quantum chemistry: Application to ground and excited states of beryllium dimer

Cornell Affiliated Author(s)
Author
Sandeep Sharma
Takeshi Yanai
George Booth
C. Umrigar
Garnet Chan
Abstract

We combine explicit correlation via the canonical transcorrelation approach with the density matrix renormalization group and initiator full configuration interaction quantum Monte Carlo methods to compute a near-exact beryllium dimer curve, without the use of composite methods. In particular, our direct density matrix renormalization group calculations produce a well-depth of De = 931.2 cm-1 which agrees very well with recent experimentally derived estimates De = 929.7±2 cm-1 [J. M. Merritt, V. E. Bondybey, and M. C. Heaven, Science 324, 1548 (2009)] and De= 934.6 cm-1 [K. Patkowski, V.

Journal
Journal of Chemical Physics
Date Published
Funding Source
NSF-CHE-1112097
NSF-CHE-1265277
1112097
1265277
25288013
Group (Lab)
Cyrus Umrigar Group

Dissipation signatures of the normal and superfluid phases in torsion pendulum experiments with He 3 in aerogel

Cornell Affiliated Author(s)
Author
N. Zhelev
R.G. Bennett
E.N. Smith
J. Pollanen
W.P. Halperin
J.M. Parpia
Abstract

We present data for the energy dissipation factor Q-1 over a broad temperature range at various pressures of a torsion pendulum setup used to study He3 confined in a 98% open silica aerogel. Values for Q-1 above Tc are temperature independent and have weak pressure dependence. Below Tc, a deliberate axial compression of the aerogel by 10% widens the range of metastability for a superfluid equal spin pairing (ESP) state; we observe this ESP phase on cooling and the B phase on warming over an extended temperature region.

Journal
Physical Review B - Condensed Matter and Materials Physics
Date Published
Funding Source
DMR-1202991
1103625
1202991
Group (Lab)
Jeevak Parpia Group