Intrinsic Electron Beam Emittance from Metal Photocathodes: The Effect of the Electron Effective MassRickman, B.; Berger, Joel; Nicholls, A.; Schroeder, W.
doi: 10.1103/PhysRevLett.111.237401pmid: 24476300
A theoretical development of prior analyses, together with our solenoid scan measurements on <?format ?>eight planar metal photocathodes (Ag, Be, Cr, Cu, Mo, Sn, Ta, and W) and previous data on Mg <?format ?>( X. J. Wang , M. Babzien , R. Malone , and Z. Wu , in Proceedings of LINAC2002, Gyeongju, Korea, 2002 <?format ?>( Pohang Accelerator Laboratory , Pohang, Korea, 2002 ), pp. 142–144 . ) indicate that the transverse momentum (and hence intrinsic emittance) of an electron beam is fundamentally dependent on the electron effective mass in the metal.
Superfluid Stiffness of a Driven Dissipative Condensate with DisorderJanot, Alexander ; Hyart, Timo ; Eastham, Paul R; Rosenow, Bernd R
doi: 10.1103/PhysRevLett.111.230403pmid: 24476236
Observations of macroscopic quantum coherence in driven systems, e.g. polariton condensates, have strongly stimulated experimental as well as theoretical efforts during the last decade. We address the question of whether a driven quantum condensate is a superfluid, allowing for the effects of disorder and its nonequilibrium nature. We predict that for spatial dimensions d < 4 the superfluid stiffness vanishes once the condensate exceeds a critical size, and treat in detail the case d = 2 . Thus a nonequilibrium condensate is not a superfluid in the thermodynamic limit, even for weak disorder, although superfluid behavior would persist in small systems.
Bogomol’nyi-Prasad-Sommerfield Skyrme Model and Nuclear Binding EnergiesAdam, C.; Naya, C.; Sanchez-Guillen, J.; Wereszczynski, A.
doi: 10.1103/PhysRevLett.111.232501pmid: 24476261
We use the classical Bogomol’nyi-Prasad-Sommerfield (BPS) soliton solutions of the BPS Skyrme model together with corrections from the collective coordinate quantization of spin and isospin, the electrostatic Coulomb energies, and a small explicit breaking of the isospin symmetry—accounting for the proton-neutron mass difference—to calculate nuclear binding energies. We find that the resulting binding energies are already in excellent agreement with their physical values for heavier nuclei, demonstrating thereby that the BPS Skyrme model is a distinguished starting point for a detailed quantitative investigation of nuclear and low-energy strong interaction physics.
Nonlocal Rheology of Granular Flows across Yield ConditionsBouzid, Mehdi; Trulsson, Martin; Claudin, Philippe; Clément, Eric; Andreotti, Bruno
doi: 10.1103/PhysRevLett.111.238301pmid: 24476308
The rheology of dense granular flows is studied numerically in a shear cell controlled at constant pressure and shear stress, confined between two granular shear flows. We show that a liquid state can be achieved even far below the yield stress, whose flow can be described with the same rheology as above the yield stress. A nonlocal constitutive relation is derived from dimensional analysis through a gradient expansion and calibrated using the spatial relaxation of velocity profiles observed under homogeneous stresses. Both for frictional and frictionless grains, the relaxation length is found to diverge as the inverse square root of the distance to the yield point, on both sides of that point.
Physicochemical Basis for Water-Actuated Movement and Stress Generation <?format ?>in Nonliving Plant TissuesBertinetti, L.; Fischer, F.; Fratzl, P.
doi: 10.1103/PhysRevLett.111.238001pmid: 24476305
Generating stresses and strains through water uptake from atmospheric humidity is a common process in nature, e.g., in seed dispersal. Actuation depends on a balance between chemical interactions and the elastic energy required to accomplish the volume change. In order to study the poorly understood chemical interactions, we combine mechanosorption experiments with theoretical calculations of the swelling behavior to estimate the mechanical energy and extract the contribution of the chemical energy per absorbed water molecule. The latter is highest in the completely dry state and stays almost constant at about 1.2 kT for higher hydrations. This suggests that water bound to the macromolecular components of the wood tissues acquires one additional hydrogen bond per eight water molecules, thus providing energy for actuation.
Broadening the Cloaking Bandwidth with Non-Foster MetasurfacesChen, Pai-Yen; Argyropoulos, Christos; Alù, Andrea
doi: 10.1103/PhysRevLett.111.233001pmid: 24476265
We introduce the concept and practical design of broadband, ultrathin cloaks based on non-Foster, negatively capacitive metasurfaces. By using properly tailored, active frequency-selective screens conformal to an object, within the realm of a practical realization, we show that it is possible to drastically reduce the scattering over a wide frequency range in the microwave regime, orders of magnitude broader than any available passive cloaking technology. The proposed active cloak may impact not only invisibility and camouflaging, but also practical antenna and sensing applications.
Scaling Laws of Structural LubricityDietzel, Dirk; Feldmann, Michael; Schwarz, Udo; Fuchs, Harald; Schirmeisen, André
doi: 10.1103/PhysRevLett.111.235502pmid: 24476292
“Structural lubricity” refers to a unique friction state in which two flat surfaces are sliding past each other with ultralow resistance due to incommensurate atomic lattice structures. In this case, theory anticipates sublinear scaling for the area dependence of friction. Here, we experimentally confirm these predictions by measuring the sliding resistance of amorphous antimony and crystalline gold nanoparticles on crystalline graphite. For the amorphous particles a square root relation between friction and contact area is observed. For crystalline gold particles we find a more complex scaling behavior related to variations in particle shape and orientation. These results allow us to link mesoscopic friction to atomic principles.