Impact of the capping layers on lateral confinement in InAs/InP quantum dots for 1.55 um laser applications srudied by magneto-photoluminescence.

We have used magnetophotoluminescence to study the impact of different capping layer material combinations (InP, GaInAsP quaternary alloy, or both InP and quaternary alloy) on lateral confinement in InAs/InP quantum dots (QDs) grown on (311)B orientated substrates. Exciton effective masses, Bohr radii, and binding energies are measured for these samples. Conclusions regarding the strength of the lateral confinement in the different samples are supported by photoluminescence at high excitation power. Contrary to theoretical predictions, InAs QDs in quaternary alloy are found to have better confinement properties than InAs/InP QDs. This is attributed to a lack of lateral intermixing with the quaternary alloy, which is present when InP is used to (partially) cap the dots. The implications of the results for reducing the temperature sensitivity of QD lasers are discussed. ©2005 American Institute of Physic

High-resolution stratigraphy of the Newark rift basin (early Mesozoic, eastern North America)

Virtually the entire Late Triassic and earliest Jurassic age section of the early Mesozoic Newark continental rift basin has been recovered in over 6770 m of continuous core as part of the Newark Basin Coring Project (NBCP). Core was collected using an offset drilling method at seven sites in the central part of the basin. The cores span most of the fluvial Stockton Formation, all of the lacustrine Lockatong and Passaic formations, the Orange Mountain Basalt, and nearly all of the lacustrine Feltville Formation. The cores allow for the first time the full Triassic-age part of the Newark basin stratigraphic sequence to be described in detail. This includes the gray, purple, and red, mostly fluvial Stockton Formation as well as the 53 members that make up the lacustrine Lockatong (mostly gray and black) and Passaic (mostly red) formations. The nearly 25% overlap zones between each of the stratigraphically adjacent cores are used to test lateral correlations in detail, scale the cores to one another, and combine them in a 4660-m-thick composite section. This composite shows that the entire post-Stockton sedimentary section consists of a hierarchy of sedimentary cycles, thought to be of Milankovitch climate cycle origin. Lithostratigraphic and magnetostratigraphic correlations between core overlap zones and outcrops demonstrate that the individual sedimentary cycles can be traced essentially basinwide. The agreement between the cyclostratigraphy and magnetostratigraphy shows both the cycles and the polarity boundaries to be isochronous horizons. Detailed analysis of the Newark basin shows that high-resolution cyclostratigraphy is possible in lacustrine, primarily red-bed rift sequences and provides a fine-scale framework for global correlations and an understanding of continental tropical climate change

Cosmic Rays and Large Extra Dimensions

We have proposed that the cosmic ray spectrum "knee", the steepening of the cosmic ray spectrum at energy E \gsim 10^{15.5} eV, is due to "new physics", namely new interactions at TeV cm energies which produce particles undetected by the experimental apparatus. In this letter we examine specifically the possibility that this interaction is low scale gravity. We consider that the graviton propagates, besides the usual four dimensions, into an additional $\delta$, compactified, large dimensions and we estimate the graviton production in $p p$ collisions in the high energy approximation where graviton emission is factorized. We find that the cross section for graviton production rises as fast as $(\sqrt{s}/M_f)^{2+\delta}$, where $M_f$ is the fundamental scale of gravity in $4+\delta$ dimensions, and that the distribution of radiating a fraction $y$ of the initial particle's energy into gravitational energy (which goes undetected) behaves as $\delta y^{\delta -1}$. The missing energy leads to an underestimate of the true energy and generates a break in the {\sl inferred} cosmic ray spectrum (the "kne"). By fitting the cosmic ray spectrum data we deduce that the favorite values for the parameters of the theory are $M_f \sim 8$ TeV and $\delta =4$.Comment: 8 pages, 1 figur

Measuring High Energy Neutrino-Nucleon Cross Sections With Future Neutrino Telescopes

Next generation kilometer-scale neutrino telescopes, such as ICECUBE, can test standard model predictions for neutrino-nucleon cross sections at energies well beyond the reach of collider experiments. At energies near a PeV and higher, the Earth becomes opaque to neutrinos. At these energies, the ratio of upgoing and downgoing events can be used to measure the total neutrino-nucleon cross section given the presence of an adequate high energy neutrino flux.Comment: 4 pages, 5 figure

A Global Diatom Database- Abundance, Biovolume and Biomass in the World Ocean

Phytoplankton identification and abundance data are now commonly feeding plankton distribution databases worldwide. This study is a first attempt to compile the largest possible body of data available from different databases as well as from individual published or unpublished datasets regarding diatom distribution in the world ocean. The data obtained originate from time series studies as well as spatial studies. This effort is supported by the Marine Ecosystem Model Inter-Comparison Project (MAREMIP), which aims at building consistent datasets for the main plankton functional types (PFTs) in order to help validate biogeochemical ocean models by using carbon (C) biomass derived from abundance data. In this study we collected over 293 000 individual geo-referenced data points with diatom abundances from bottle and net sampling. Sampling site distribution was not homogeneous, with 58% of data in the Atlantic, 20% in the Arctic, 12% in the Pacific, 8% in the Indian and 1% in the Southern Ocean. A total of 136 different genera and 607 different species were identified after spell checking and name correction. Only a small fraction of these data were also documented for biovolumes and an even smaller fraction was converted to C biomass. As it is virtually impossible to reconstruct everyone\u27s method for biovolume calculation, which is usually not indicated in the datasets, we decided to undertake the effort to document, for every distinct species, the minimum and maximum cell dimensions, and to convert all the available abundance data into biovolumes and C biomass using a single standardized method. Statistical correction of the database was also adopted to exclude potential outliers and suspicious data points. The final database contains 90 648 data points with converted C biomass. Diatom C biomass calculated from cell sizes spans over eight orders of magnitude. The mean diatom biomass for individual locations, dates and depths is 141.19 μg Cl-1, while the median value is 11.16 μg Cl-1. Regarding biomass distribution, 19% of data are in the range 0-1 μg Cl-1, 29% in the range 1-10 μg Cl-1, 31% in the range 10-100 μg Cl-1, 18% in the range 100-1000 μg Cl-1, and only 3% \u3e 1000 μg Cl-1. Interestingly, less than 50 species contributed to \u3e90% of global biomass, among which centric species were dominant. Thus, placing significant efforts on cell size measurements, process studies and C quota calculations of these species should considerably improve biomass estimates in the upcoming years. A first-order estimate of the diatom biomass for the global ocean ranges from 444 to 582 Tg C, which converts to 3 to 4 Tmol Si and to an average Si biomass turnover rate of 0.15 to 0.19 d-1. Link to the dataset: doi:10.1594/PANGAEA.777384

Angular Dependence of Neutrino Flux in KM3 Detectors in Low Scale Gravity Models

Cubic kilometer neutrino telescopes are capable of probing fundamental questions of ultra-high energy neutrino interactions. There is currently great interest in neutrino interactions caused by low-scale, extra dimension models. Above 1 PeV the cross section in low scale gravity models rises well above the total Standard Model cross section. We assess the observability of this effect in the 1 PeV - 100 PeV energy range of kilometer-scale detectors with several new points of emphasis that hinge on enhanced neutral current cross sections. A major point is the importance of ``feed-down'' regeneration of upward neutrino flux, driven by new-physics neutral current interactions in the flux evolution equations. Feed-down is far from negligible, and it is essential to include its effect. We then find that the angular distribution of events has high discriminating value in separating models. In particular the ``up-to-down'' ratio between upward and downward-moving neutrino fluxes is a practical diagnostic tool which can discriminate between models in the near future. The slope of the angular distribution, in the region of maximum detected flux, is also substantially different in low-scale gravity and the Standard Model. These observables are only weakly dependent on astrophysical flux uncertainties. We conclude that angular distributions can reveal a breakdown of the Standard Model and probe the new physics beyond, as soon as data become available.Comment: 25 pages, 6 figures, discussion of calculations expanded, references adde

Cartography with Accelerators: Locating Fermions in Extra Dimensions at Future Lepton Colliders

In the model of Arkani-Hamed and Schmaltz the various chiral fermions of the Standard Model(SM) are localized at different points on a thick wall which forms an extra dimension. Such a scenario provides a way of understanding the absence of proton decay and the fermion mass hierarchy in models with extra dimensions. In this paper we explore the capability of future lepton colliders to determine the location of these fermions in the extra dimension through precision measurements of conventional scattering processes both below and on top of the lowest lying Kaluza-Klein gauge boson resonance. We show that for some classes of models the locations of these fermions can be very precisely determined while in others only their relative positions can be well measured.Comment: 32 pages, 10 figs, LaTe

Ultra high energy neutrino-nucleon cross section from cosmic ray experiments and neutrino telescopes

We deduce the cosmogenic neutrino flux by jointly analysing ultra high energy cosmic ray data from HiRes-I and II, AGASA and the Pierre Auger Observatory. We make two determinations of the neutrino flux by using a model-dependent method and a model-independent method. The former is well-known, and involves the use of a power-law injection spectrum. The latter is a regularized unfolding procedure. We then use neutrino flux bounds obtained by the RICE experiment to constrain the neutrino-nucleon inelastic cross section at energies inaccessible at colliders. The cross section bounds obtained using the cosmogenic fluxes derived by unfolding are the most model-independent bounds to date.Comment: 20 pages, 6 figures, 2 table