Dynamic Models of Reputation and Competition in Job-Market Matching

A fundamental decision faced by a firm hiring employees - and a familiar one to anyone who has dealt with the academic job market, for example - is deciding what caliber of candidates to pursue. Should the firm try to increase its reputation by making offers to higher-quality candidates, despite the risk that the candidates might reject the offers and leave the firm empty-handed? Or should it concentrate on weaker candidates who are more likely to accept the offer? The question acquires an added level of complexity once we take into account the effect one hiring cycle has on the next: hiring better employees in the current cycle increases the firm's reputation, which in turn increases its attractiveness for higher-quality candidates in the next hiring cycle. These considerations introduce an interesting temporal dynamic aspect to the rich line of research on matching models for job markets, in which long-range planning and evolving reputational effects enter into the strategic decisions made by competing firms. We develop a model based on two competing firms to try capturing as cleanly as possible the elements that we believe constitute the strategic tension at the core of the problem: the trade-off between short-term recruiting success and long-range reputation-building; the inefficiency that results from underemployment of people who are not ranked highest; and the influence of earlier accidental outcomes on long-term reputations. Our model exhibits all these phenomena in a stylized setting, governed by a parameter q that captures the difference in strength between the two top candidates in each hiring cycle. We show that when q is relatively low the efficiency of the job market is improved by long-range reputational effects, but when q is relatively high, taking future reputations into account can sometimes reduce the efficiency

Polyelectrolyte Multilayering on a Charged Planar Surface

The adsorption of highly \textit{oppositely} charged flexible polyelectrolytes (PEs) on a charged planar substrate is investigated by means of Monte Carlo (MC) simulations. We study in detail the equilibrium structure of the first few PE layers. The influence of the chain length and of a (extra) non-electrostatic short range attraction between the polycations and the negatively charged substrate is considered. We show that the stability as well as the microstructure of the PE layers are especially sensitive to the strength of this latter interaction. Qualitative agreement is reached with some recent experiments.Comment: 28 pages; 11 (main) Figs - Revtex4 - Higher resolution Figs can be obtained upon request. To appear in Macromolecule

The effect of size ratio on the sphere structure factor in colloidal sphere-plate mixtures

The following article appeared in Journal of Chemical Physics 137.20 (2012): 204909 and may be found at http://scitation.aip.org/content/aip/journal/jcp/137/20/10.1063/1.4767722Binary mixtures of colloidal particles of sufficiently different sizes or shapes tend to demix at high concentration. Already at low concentration, excluded volume interactions between the two species give rise to structuring effects. Here, a new theoretical description is proposed of the structure of colloidal sphere-plate mixtures, based on a density expansion of the work needed to insert a pair of spheres and a single sphere in a sea of them, in the presence or not of plates. The theory is first validated using computer simulations. The predictions are then compared to experimental observations using silica spheres and gibbsite platelets. Small-angle neutron scattering was used to determine the change of the structure factor of spheres on addition of platelets, under solvent contrast conditions where the platelets were invisible. Theory and experiment agreed very well for a platelet/sphere diameter ratio Dd 2.2 and reasonably well for Dd 5. The sphere structure factor increases at low scattering vector Q in the presence of platelets; a weak reduction of the sphere structure factor was predicted at larger Q, and for the system with Dd 2.2 was indeed observed experimentally. At fixed particle volume fraction, an increase in diameter ratio leads to a large change in structure factor. Systems with a larger diameter ratio also phase separate at lower concentrationsG. Cinacchi was supported by the EU through a Marie Curie Research Fellowship PIEF-GA-2008-220557 and now by the Ministry of Research of Spain through the Ramón y Cajal contract (Contract. No. RYC-2010-07475). N. Doshi was jointly supported by Imerys and EPSRC DTA. Experiments at ILL were supported by beamtime allocations 9-12- 216 and 9-10-1044. Materials were kindly donated by AZ Electronics (Klebosol) and Lubrizol (Solsperse 41000

The Self-Administered Witness Interview Tool (SAW-IT): Enhancing witness recall of workplace incidents

Given the often crucial role of witness evidence in Occupational Health and Safety investigation, statements should be obtained as soon as possible after an incident using best practice methods. The present research systematically tested the efficacy of a novel Self-Administered Witness Interview Tool (SAW-IT); an adapted version of the Self-Administered Interview (SAI©) designed to elicit comprehensive information from witnesses to industrial events. The present study also examined whether completing the SAW-IT mitigated the effect of schematic processing on witness recall. Results indicate that the SAW-IT elicited significantly more correct details, as well as more precise information than a traditional incident report form. Neither the traditional report from, nor the SAW-IT mitigated against biasing effects of contextual information about a worker’s safety history, confirming that witnesses should be shielded from extraneous post-event information prior to reporting. Importantly, these results demonstrate that the SAW-IT can enhance the quality of witness reports

Quantum computing with antiferromagnetic spin clusters

We show that a wide range of spin clusters with antiferromagnetic intracluster exchange interaction allows one to define a qubit. For these spin cluster qubits, initialization, quantum gate operation, and readout are possible using the same techniques as for single spins. Quantum gate operation for the spin cluster qubit does not require control over the intracluster exchange interaction. Electric and magnetic fields necessary to effect quantum gates need only be controlled on the length scale of the spin cluster rather than the scale for a single spin. Here, we calculate the energy gap separating the logical qubit states from the next excited state and the matrix elements which determine quantum gate operation times. We discuss spin cluster qubits formed by one- and two-dimensional arrays of s=1/2 spins as well as clusters formed by spins s>1/2. We illustrate the advantages of spin cluster qubits for various suggested implementations of spin qubits and analyze the scaling of decoherence time with spin cluster size.Comment: 15 pages, 7 figures; minor change

Bi-stable tunneling current through a molecular quantum dot

An exact solution is presented for tunneling through a negative-U d-fold degenerate molecular quantum dot weakly coupled to electrical leads. The tunnel current exhibits hysteresis if the level degeneracy of the negative-U dot is larger than two (d>2). Switching occurs in the voltage range V1 < V < V2 as a result of attractive electron correlations in the molecule, which open up a new conducting channel when the voltage is above the threshold bias voltage V2. Once this current has been established, the extra channel remains open as the voltage is reduced down to the lower threshold voltage V1. Possible realizations of the bi-stable molecular quantum dots are fullerenes, especially C60, and mixed-valence compounds.Comment: 5 pages, 1 figure. (v2) Figure updated to compare the current hysteresis for degeneracies d=4 and d>>1 of the level in the dot, minor corrections in the text. To appear in Phys. Rev.