An Empirical Study of Price Dispersion in Homogenous Goods Markets

This paper presents the results of an empirical study of price dispersion in homogeneous goods markets. Modern economic theory suggests that inevitable asymmetries of information in markets lead to an equilibrium in which price dispersion is present even when goods are perfectly homogenous. In this paper we present an empirical analysis in which we employ both cross-sectional and time-series data gathered directly from Pricegrabber.com, one of the most popular and comprehensive online shopping/price-comparison sites on the Internet. In particular our analysis focuses on (i) the effect that the number of firms offering a good has on price dispersion, (ii) the informational value to the consumer of using the Pricegrabber website, and (iii) the persistency of price dispersion over time.E-commerce, Internet marketing, Price dispersion, Signaling, Search Cost, Gatekeepers, Regression and other statistical techniques JEL Classification: L81, L86, L11

Thermal induced unfolding refolding of a nucleocapsid COVN protein

Unfolding of a coarse grained COVN protein from its native configuration shows a linear response with increasing temperature followed by a nonmonotonic double peaks in its radius of gyration. The protein conforms to a random coil of folded segments in native state with increasing tenuous and globular structures in specific temperature regimes where the effective dimensions of corresponding structures D is about 1.6 to 2.4. Thermal agitation alone is not sufficient to fully eradicate its segmental folding as few folds are found to persist around such residues as 65W, 110Y, 224L, 374P even at high temperatures.Comment: 8 pages, 5 figure

Pinning the conformation of a protein (CorA) in a solute matrix with selective binding

Conformation of a protein (CorA) is examined in a matrix with mobile solute constituents as a function of solute-residue interaction strength (f) by a coarse-grained model with a Monte Carlo simulation. Solute particles are found to reach their targeted residue due to their unique interactions with the residues. Degree of slowing down of the protein depends on the interaction strength f. Unlike a predictable dependence of the radius of gyration of the same protein on interaction in an effective medium, it does not show a systematic dependence on interaction due to pinning caused by the solute binding. Spread of the protein chain is quantified by estimating its effective dimension (D) from scaling of the structure factor. Even with a lower solute-residue interaction, the protein chain appears to conform to a random-coil conformation (D ~ 2) in its native phase where it is globular in absence of such solute environment. The structural spread at small length scale differs from that at large scale in presence of stronger interactions: D ~ 2.3 at smaller length scale and D ~ 1.4 on larger scale with f = 3.5 while D ~ 1.4 at smaller length scale and D ~ 2.5 at larger length scales with f = 4.0

Spin injection in Silicon at zero magnetic field

In this letter, we show efficient electrical spin injection into a SiGe based \textit{p-i-n} light emitting diode from the remanent state of a perpendicularly magnetized ferromagnetic contact. Electron spin injection is carried out through an alumina tunnel barrier from a Co/Pt thin film exhibiting a strong out-of-plane anisotropy. The electrons spin polarization is then analysed through the circular polarization of emitted light. All the light polarization measurements are performed without an external applied magnetic field \textit{i.e.} in remanent magnetic states. The light polarization as a function of the magnetic field closely traces the out-of-plane magnetization of the Co/Pt injector. We could achieve a circular polarization degree of the emitted light of 3 % at 5 K. Moreover this light polarization remains almost constant at least up to 200 K.Comment: accepted in AP

Does Infall End Before the Class I Stage?

We have observed HCO+ J=3-2 toward 16 Class I sources and 18 Class 0 sources, many of which were selected from Mardones et al. (1997). Eight sources have profiles significantly skewed to the blue relative to optically thin lines. We suggest six sources as new infall candidates. We find an equal "blue excess" among Class 0 and Class I sources after combining this sample with that of Gregersen et al. (1997). We used a Monte Carlo code to simulate the temporal evolution of line profiles of optically thick lines of HCO+, CS and H2CO in a collapsing cloud and found that HCO+ had the strongest asymmetry at late times. If a blue-peaked line profile implies infall, then the dividing line between the two classes does not trace the end of the infall stage.Comment: 21 pages, 8 figures, accepted by ApJ for April 20, 2000, added acknowledgmen

Turbulence driven by outflow-blown cavities in the molecular cloud of NGC 1333

Outflows from young stellar objects have been identified as a possible source of turbulence in molecular clouds. To investigate the relationship between outflows, cloud dynamics and turbulence, we compare the kinematics of the molecular gas associated with NGC 1333, traced in 13CO(1-0), with the distribution of young stellar objects (YSOs) within. We find a velocity dispersion of ~ 1-1.6 km/s in 13CO that does not significantly vary across the cloud, and is uncorrelated with the number of nearby young stellar outflows identified from optical and submillimeter observations. However, from velocity channel maps we identify about 20 cavities or depressions in the 13CO intensity of scales > 0.1-0.2 pc and velocity widths 1-3 km/s. The cavities exhibit limb brightened rims in both individual velocity channel maps and position velocity diagrams, suggesting that they are slowly expanding. We interpret these cavities to be remnants of past YSO outflow activity: If these cavities are presently empty, they would fill in on time scales of a million years. This can exceed the lifetime of a YSO outflow phase, or the transit time of the central star through the cavity, explaining the the absence of any clear correlation between the cavities and YSO outflows. We find that the momentum and energy deposition associated with the expansion of the cavities is sufficient to power the turbulence in the cloud. In this way we conclude that the cavities are an important intermediary step between the conversion of YSO outflow energy and momentum into cloud turbulent motions.Comment: Accepted for publication in ApJ. Check out http://astro.pas.rochester.edu/~aquillen/coolpics.html for channel map and PosVel movies of N133

Can Protostellar Jets Drive Supersonic Turbulence in Molecular Clouds?

Jets and outflows from young stellar objects are proposed candidates to drive supersonic turbulence in molecular clouds. Here, we present the results from multi-dimensional jet simulations where we investigate in detail the energy and momentum deposition from jets into their surrounding environment and quantify the character of the excited turbulence with velocity probability density functions. Our study include jet--clump interaction, transient jets, and magnetised jets. We find that collimated supersonic jets do not excite supersonic motions far from the vicinity of the jet. Supersonic fluctuations are damped quickly and do not spread into the parent cloud. Instead subsonic, non-compressional modes occupy most of the excited volume. This is a generic feature which can not be fully circumvented by overdense jets or magnetic fields. Nevertheless, jets are able to leave strong imprints in their cloud structure and can disrupt dense clumps. Our results question the ability of collimated jets to sustain supersonic turbulence in molecular clouds.Comment: 33 pages, 18 figures, accepted by ApJ, version with high resolution figures at: http://www.ita.uni-heidelberg.de/~banerjee/publications/jet_paper.pd

Spitzer Observations of NGC 1333: A Study of Structure and Evolution in a Nearby Embedded Cluster

We present a comprehensive analysis of structure in the young, embedded cluster, NGC 1333 using members identified with Spitzer and 2MASS photometry based on their IR-excess emission. In total, 137 members are identified in this way, composed of 39 protostars and 98 more evolved pre-main sequence stars with disks. Of the latter class, four are transition/debris disk candidates. The fraction of exposed pre-main sequence stars with disks is 83% +/- 11%, showing that there is a measurable diskless pre-main sequence population. The sources in each of the Class I and Class II evolutionary states are shown to have very different spatial distributions relative to the distribution of the dense gas in their natal cloud. However, the distribution of nearest neighbor spacings among these two groups of sources are found to be quite similar, with a strong peak at spacings of 0.045 pc. Radial and azimuthal density profiles and surface density maps computed from the identified YSOs show that NGC 1333 is elongated and not strongly centrally concentrated, confirming previous claims in the literature. We interpret these new results as signs of a low velocity dispersion, extremely young cluster that is not in virial equilibrium.Comment: 59 pages, 20 figures, accepted to ApJ, verion with full resolution figures available at http://www.cfa.harvard.edu/~rgutermuth/preprints/gutermuth_ngc1333.pdf . Updated to fix astro-ph figure garblin