The Stability of Adsorbates Imaged with a Scanning Tunneling Microscope Using Hopping Versus Constant Current Scanning

We have studied the stability of various adsorbates, including gold, a platinum-iridium alloy, and DNA, on monoatomically flat gold imaged with a scanning tunneling microscope. We find that adsorbates are generally more stable, sometimes dramatically so, if imaged with a hopping trajectory of the tip rather than with the conventional constant-current scanning technique. Gold pits and associated debris formed on flat gold surfaces under saline solution by mechanical impact of the tip with the surface are always much more stable when imaged with hopping. Samples of thin, sub-monoatomic layers (0.1 nm and 0.2 nm thick) of a platinum-iridium alloy evaporated onto gold and imaged in air were not stable with either imaging method but were much noisier with constant-current scanning; samples of thick layers (20 nm and 50 nm) were stable with both methods, while layers 1 and 2 nm thick were generally stable with hopping and usually unstable with constant-current scanning. DNA deposited onto gold as an aqueous solution and then air-dried was usually not stable enough to resolve molecular features with either scanning method, though adsorbed aggregates generally showed stable large-scale structure with hopping but were very unstable with constant-current scanning

Application of Swept-Sine Excitation for Acoustic Impedance Education

The NASA Langley Normal Incidence Tube (NIT) and Grazing Flow Impedance Tube (GFIT) are regularly employed to characterize the frequency response of acoustic liners through the eduction of their specific acoustic impedance. Both test rigs typically use an acoustic source that produces sine wave signals at discrete frequencies (Stepped-Sine) to educe the impedance. The current work details a novel approach using frequency-swept sine waveforms normalized to a constant sound pressure level for excitation. Determination of the sound pressure level and phase from microphone measurements acquired using swept-sine excitation is performed using a modified Vold-Kalman order tracking filter. Four acoustic liners are evaluated in the NIT and GFIT with both stepped-sine and swept-sine sources. Using these two methods, the educed impedance spectra are shown to compare favorably. However, the new (Swept-Sine) approach provides much greater frequency resolution in less time, allowing the acoustic liner properties to be studied in much greater detail

Student input-A case of an extended flipped classroom

© 2017 IEEE. The idea from Socrates about the knowledge being a part of the students' knowledge base or ability of combining accessible knowledge forms the backdrop for how the most recent course in Knowledge Management (spring of 2017) was conducted. The course is 7,5 ECTS and the students are primarily adults in a worklife. The course is net and seminar based, with three seminars per semester. During the seminars the concept of Flipped Classroom is used. This means that the students are provided with a recorded lecture in beforehand and only highlights are presented. The rest of the time during the seminar is used to activate the students through tasks and problem solving. However, the tasks are not predefined and prefabricated. The way this course is structured, the students themselves are giving the input to the tasks and assignments. This is based on the idea that the students themselves, coming from a worklife where knowledge management is a part of their every day worklife, should reflect upon their own practice. Also, it is important to share knowledge and by utilizing each students own experiences it is possible to enrich the 'database' of cases or tasks for the students to solve and work with in order to incorporate the new theory from the course curriculum. Basing the problem solving on student input provide the lecturer AND the students with a richer knowledge base and case portfolio. This does, however, require some effort from the lecturers side. The input from the students are generally key words and fragments. The session is facilitated by the lecturer, encouraging the students to bring forward own experiences or situations they would like resolved, either real or fiction. The key words and fragments are discussed amongst the students and the lecturer makes notes on a blackboard or on a digital canvas (MS PowerPoint or similar). The students are given a break and the lecturer collects the key words and synthesizes this into a case. Upon the return of the students, they solve the cases in groups and discuss possible solutions and what theory that apply to the different aspects of the case. Then a plenary session is facilitated where a suggested solution is developed. During a one-day seminar three to four cases are developed as a 'joint venture' amongst the students and the lecturer. The feedback from the students is very positive. They claim that this way of working strongly contributes to an enhanced learning outcome. Some students also report on utilizing knowledge acquired at these seminars back at their workplace. These are some results from the survey and interviews. This research will be presented in detail in the paper. We will also elaborate on how this way of flipping the classroom can be utilized in different courses and areas

Crossover effects in a discrete deposition model with Kardar-Parisi-Zhang scaling

We simulated a growth model in 1+1 dimensions in which particles are aggregated according to the rules of ballistic deposition with probability p or according to the rules of random deposition with surface relaxation (Family model) with probability 1-p. For any p>0, this system is in the Kardar-Parisi-Zhang (KPZ) universality class, but it presents a slow crossover from the Edwards-Wilkinson class (EW) for small p. From the scaling of the growth velocity, the parameter p is connected to the coefficient of the nonlinear term of the KPZ equation, lambda, giving lambda ~ p^gamma, with gamma = 2.1 +- 0.2. Our numerical results confirm the interface width scaling in the growth regime as W ~ lambda^beta t^beta, and the scaling of the saturation time as tau ~ lambda^(-1) L^z, with the expected exponents beta =1/3 and z=3/2 and strong corrections to scaling for small lambda. This picture is consistent with a crossover time from EW to KPZ growth in the form t_c ~ lambda^(-4) ~ p^(-8), in agreement with scaling theories and renormalization group analysis. Some consequences of the slow crossover in this problem are discussed and may help investigations of more complex models.Comment: 16 pages, 7 figures; to appear in Phys. Rev.

Nucleon Edm from Atomic Systems and Constraints on Supersymmetry Parameters

The nucleon EDM is shown to be directly related to the EDM of atomic systems. From the observed EDM values of the atomic Hg system, the neutron EDM can be extracted, which gives a very stringent constraint on the supersymmetry parameters. It is also shown that the measurement of Nitrogen and Thallium atomic systems should provide important information on the flavor dependence of the quark EDM. We perform numerical analyses on the EDM of neutron, proton and electron in the minimal supersymmetric standard model with CP-violating phases. We demonstrate that the new limit on the neutron EDM extracted from atomic systems excludes a wide parameter region of supersymmetry breaking masses above 1 TeV, while the old limit excludes only a small mass region below 1 TeV.Comment: 10 pages, 7 figure file

Scaling Behavior of Cyclical Surface Growth

The scaling behavior of cyclical surface growth (e.g. deposition/desorption), with the number of cycles n, is investigated. The roughness of surfaces grown by two linear primary processes follows a scaling behavior with asymptotic exponents inherited from the dominant process while the effective amplitudes are determined by both. Relevant non-linear effects in the primary processes may remain so or be rendered irrelevant. Numerical simulations for several pairs of generic primary processes confirm these conclusions. Experimental results for the surface roughness during cyclical electrodeposition/dissolution of silver show a power-law dependence on n, consistent with the scaling description.Comment: 2 figures adde

A simulational and theoretical study of the spherical electrical double layer for a size-asymmetric electrolyte: the case of big coions

Monte Carlo simulations of a spherical macroion, surrounded by a size-asymmetric electrolyte in the primitive model, were performed. We considered 1:1 and 2:2 salts with a size ratio of 2 (i.e., with coions twice the size of counterions), for several surface charge densities of the macrosphere. The radial distribution functions, electrostatic potential at the Helmholtz surfaces, and integrated charge are reported. We compare these simulational data with original results obtained from the Ornstein-Zernike integral equation, supplemented by the hypernetted chain/hypernetted chain (HNC/HNC) and hypernetted chain/mean spherical approximation (HNC/MSA) closures, and with the corresponding calculations using the modified Gouy-Chapman and unequal-radius modified Gouy-Chapman theories. The HNC/HNC and HNC/MSA integral equations formalisms show good concordance with Monte Carlo "experiments", whereas the notable limitations of point-ion approaches are evidenced. Most importantly, the simulations confirm our previous theoretical predictions of the non-dominance of the counterions in the size-asymmetric spherical electrical double layer [J. Chem. Phys. 123, 034703 (2005)], the appearance of anomalous curvatures at the outer Helmholtz plane and the enhancement of charge reversal and screening at high colloidal surface charge densities due to the ionic size asymmetry.Comment: 11 pages, 7 figure

Growth model with restricted surface relaxation

We simulate a growth model with restricted surface relaxation process in d=1 and d=2, where d is the dimensionality of a flat substrate. In this model, each particle can relax on the surface to a local minimum, as the Edwards-Wilkinson linear model, but only within a distance s. If the local minimum is out from this distance, the particle evaporates through a refuse mechanism similar to the Kim-Kosterlitz nonlinear model. In d=1, the growth exponent beta, measured from the temporal behavior of roughness, indicates that in the coarse-grained limit, the linear term of the Kardar-Parisi-Zhang equation dominates in short times (low-roughness) and, in asymptotic times, the nonlinear term prevails. The crossover between linear and nonlinear behaviors occurs in a characteristic time t_c which only depends on the magnitude of the parameter s, related to the nonlinear term. In d=2, we find indications of a similar crossover, that is, logarithmic temporal behavior of roughness in short times and power law behavior in asymptotic times

Collective T- and P- Odd Electromagnetic Moments in Nuclei with Octupole Deformations

Parity and time invariance violating forces produce collective P- and T- odd moments in nuclei with static octupole deformation. Collective Schiff moment, electric octupole and dipole and also magnetic quadrupole appear due to the mixing of rotational levels of opposite parity and can exceed single-particle moments by more than a factor of 100. This enhancement is due to two factors, the collective nature of the intrinsic moments and the small energy separation between members of parity doublets. The above moments induce T- and P- odd effects in atoms and molecules. Experiments with such systems may improve substantially the limits on time reversal violation.Comment: 9 pages, Revte

Effect of Long-Range Interactions in the Conserved Kardar-Parisi-Zhang Equation

The conserved Kardar-Parisi-Zhang equation in the presence of long-range nonlinear interactions is studied by the dynamic renormalization group method. The long-range effect produces new fixed points with continuously varying exponents and gives distinct phase transitions, depending on both the long-range interaction strength and the substrate dimension $d$. The long-range interaction makes the surface width less rough than that of the short-range interaction. In particular, the surface becomes a smooth one with a negative roughness exponent at the physical dimension d=2.Comment: 4 pages(LaTex), 1 figure(Postscript