Can Everett be Interpreted Without Extravaganza?

Everett's relative states interpretation of quantum mechanics has met with problems related to probability, the preferred basis, and multiplicity. The third theme, I argue, is the most important one. It has led to developments of the original approach into many-worlds, many-minds, and decoherence-based approaches. The latter especially have been advocated in recent years, in an effort to understand multiplicity without resorting to what is often perceived as extravagant constructions. Drawing from and adding to arguments of others, I show that proponents of decoherence-based approaches have not yet succeeded in making their ontology clear.Comment: Succinct analysis forthcoming in Found. Phy

Real World Interpretations of Quantum Theory

I propose a new class of interpretations, {\it real world interpretations}, of the quantum theory of closed systems. These interpretations postulate a preferred factorization of Hilbert space and preferred projective measurements on one factor. They give a mathematical characterisation of the different possible worlds arising in an evolving closed quantum system, in which each possible world corresponds to a (generally mixed) evolving quantum state. In a realistic model, the states corresponding to different worlds should be expected to tend towards orthogonality as different possible quasiclassical structures emerge or as measurement-like interactions produce different classical outcomes. However, as the worlds have a precise mathematical definition, real world interpretations need no definition of quasiclassicality, measurement, or other concepts whose imprecision is problematic in other interpretational approaches. It is natural to postulate that precisely one world is chosen randomly, using the natural probability distribution, as the world realised in Nature, and that this world's mathematical characterisation is a complete description of reality.Comment: Minor revisions. To appear in Foundations of Physic

Recycling sediments between source and sink during a eustatic cycle: Systems of late Quaternary northwestern Gulf of Mexico Basin

The northwestern Gulf of Mexico Basin is an ideal natural laboratory to study and understand source-to-sink systems. An extensive grid of high-resolution seismic data, hundreds of sediment cores and borings and a robust chronostratigraphic framework were used to examine the evolution of late Quaternary depositional systems of the northwestern Gulf of Mexico throughout the last eustatic cycle (~125 ka to Present). The study area includes fluvial systems with a wide range of drainage basin sizes, climate settings and water and sediment discharges. Detailed paleogeographic reconstructions are used to derive volumetric estimates of sediment fluxes (Volume Accumulation Rates). The results show that the response of rivers to sea-level rise and fall varied across the region. Larger rivers, including the former Mississippi, Western Louisiana (presumably the ancestral Red River), Brazos, Colorado and Rio Grande rivers, constructed deltas that advanced across the shelf in step-wise fashion during Marine Isotope Stages (MIS) 5-2. Sediment delivery to these deltas increased during the overall sea-level fall due to increases in drainage basin area and erosion of sediment on the inner shelf, where subsidence is minimal, and transport of that sediment to the more rapidly subsiding outer shelf. The sediment supply from the Brazos River to its delta increased at least 3-fold and the supply of the Colorado River increased at least 6-fold by the late stages of sea-level fall through the lowstand. Repeated filling and purging of fluvial valleys from ~119-22 ka contributed to the episodic growth of falling-stage deltas.During the MIS 2 lowstand (~22-17 ka), the Mississippi River abandoned its falling-stage fluvial-deltaic complex on the western Louisiana shelf and drained to the Mississippi Canyon. Likewise, the Western Louisiana delta was abandoned, presumably due to merger of the Red River with the Mississippi River, terminating growth of the Western Louisiana delta. The Brazos River abandoned its MIS 3 shelf margin delta to merge with the Trinity, Sabine and Calcasieu rivers and together these rivers nourished a lowstand delta and slope fan complex. The Colorado and Rio Grande rivers behaved more as point sources of sediment to thick lowstand delta-fan complexes.Lowstand incised valleys exhibit variable morphologies that mainly reflect differences in onshore and offshore relief and the time intervals these valleys were occupied. They are deeper and wider than falling stage channel belts and are associated with a shelf-wide surface of erosion (sequence boundary).During the early MIS 1 (~17 ka to 7~10 ka) sea-level rise, the offshore incised valleys of the Calcasieu, Sabine, Trinity, Brazos, Colorado, and Rio Grande rivers were filled with sediment. The offshore valleys of smaller rivers of central Texas would not be filled until the late Holocene, mainly by highstand mud. The lower, onshore portions of east Texas incised valleys were filled with sediment mainly during the Holocene, with rates of aggradation in the larger Brazos and Colorado valleys being in step with sea-level rise. Smaller rivers filled their valleys with back-stepping fluvial, estuarine and tidal delta deposits that were offset by flooding surfaces. In general, the sediment trapping capacity of bays increased as evolving barrier islands and peninsulas slowly restricted tidal exchange with the Gulf and valley filling led to more shallow, wider bays. A widespread period of increased riverine sediment flux and delta growth is attributed to climate change during MIS 1, between ~11.5 and 8.0 ka, and occurred mainly under cool-wet climate conditions.Relatively small sea-level oscillations during the MIS 1 transgression (~17 ka to ~4.0 ka) profoundly influenced coastal evolution, as manifested by landward stepping shorelines, on the order of tens of kilometers within a few thousand years. The current barriers, strand plains and chenier plains of the study area formed at different times over the past ~8 ka, due mainly to differences in sand supply and the highly variable relief on the MIS 2 surface on which these systems formed.Modern highstand deposition on the continental shelf formed the Texas Mud Blanket, which occurs on the central Texas shelf and records a remarkable increase in fine-grained sediment supply. This increase is attributed to greater delivery of sediments from the Colorado and Brazos rivers, which had filled their lower valleys and abandoned their transgressive deltas by late Holocene time, and to an increase in westward directed winds and surface currents that delivered suspended sediments from the Mississippi River to the Texas shelf.Collectively, our results demonstrate that source-to-sink analyses in low gradient basin settings requires a long-term perspective, ideally a complete eustatic cycle, because most of the sediment that was delivered to the basin by rivers underwent more than one cycle of erosion, transport and sedimentation that was regulated by sea-level rise and fall. Climate was a secondary control. The export of sediments from the hinterland to the continental shelf was not directly in step with temperature change, but rather varied between different fluvial-deltaic systems

Gutenberg Richter and Characteristic Earthquake Behavior in Simple Mean-Field Models of Heterogeneous Faults

The statistics of earthquakes in a heterogeneous fault zone is studied analytically and numerically in the mean field version of a model for a segmented fault system in a three-dimensional elastic solid. The studies focus on the interplay between the roles of disorder, dynamical effects, and driving mechanisms. A two-parameter phase diagram is found, spanned by the amplitude of dynamical weakening (or ``overshoot'') effects (epsilon) and the normal distance (L) of the driving forces from the fault. In general, small epsilon and small L are found to produce Gutenberg-Richter type power law statistics with an exponential cutoff, while large epsilon and large L lead to a distribution of small events combined with characteristic system-size events. In a certain parameter regime the behavior is bistable, with transitions back and forth from one phase to the other on time scales determined by the fault size and other model parameters. The implications for realistic earthquake statistics are discussed.Comment: 21 pages, RevTex, 6 figures (ps, eps

The Glauber model and the heavy ion reaction cross section

We reexamine the Glauber model and calculate the total reaction cross section as a function of energy in the low and intermediate energy range, where many of the corrections in the model, are effective. The most significant effect in this energy range is by the modification of the trajectory due to the Coulomb field. The modification in the trajectory due to nuclear field is also taken into account in a self consistent way. The energy ranges in which particular corrections are effective, are quantified and it is found that when the center of mass energy of the system becomes 30 times the Coulomb barrier, none of the trajectory modification to the Glauber model is really required. The reaction cross sections for light and heavy systems, right from near coulomb barrier to intermediate energies have been calculated. The exact nuclear densities and free nucleon-nucleon (NN) cross sections have been used in the calculations. The center of mass correction which is important for light systems, has also been taken into account. There is an excellent agreement between the calculations with the modified Glauber model and the experimental data. This suggests that the heavy ion reactions in this energy range can be explained by the Glauber model in terms of free NN cross sections without incorporating any medium modification.Comment: RevTeX, 21 pages including 9 Postscript figures, submitted to Phys. Rev.

The 3-D O(4) universality class and the phase transition in two-flavor QCD

We determine the critical equation of state of the three-dimensional O(4) universality class. We first consider the small-field expansion of the effective potential (Helmholtz free energy). Then, we apply a systematic approximation scheme based on polynomial parametric representations that are valid in the whole critical regime, satisfy the correct analytic properties (Griffiths' analyticity), take into account the Goldstone singularities at the coexistence curve, and match the small-field expansion of the effective potential. From the approximate representations of the equation of state, we obtain estimates of several universal amplitude ratios. The three-dimensional O(4) universality class is expected to describe the finite-temperature chiral transition of quantum chromodynamics with two light flavors. Within this picture, the O(4) critical equation of state relates the reduced temperature, the quark masses, and the condensates around T_c in the limit of vanishing quark masses.Comment: 19 pages, 5 fig

New directions in island biogeography

Aim: Much of our current understanding of ecological and evolutionary processes comes from island research. With the increasing availability of data on distributions and phylogenetic relationships and new analytical approaches to understanding the processes that shape species distributions and interactions, a re-evaluation of this ever-interesting topic is timely. Location: Islands globally. Methods: We start by arguing that the reasons why island research has achieved so much in the past also apply to the future. We then critically assess the current state of island biogeography, focusing on recent changes in emphasis, including research featured in this special issue of Global Ecology and Biogeography. Finally, we suggest promising themes for the future. We cover both ecological and evolutionary topics, although the greater emphasis on island ecology reflects our own backgrounds and interests. Results: Much ecological theory has been directly or indirectly influenced by research on island biotas. Currently, island biogeography is renascent, with research focusing on, among other things, patterns and processes underlying species interaction networks, species coexistence and the assembly of island communities through ecological and evolutionary time. Continuing island research should provide additional insight into biological invasions and other impacts of human activities, functional diversity and ecosystem functioning, extinction and diversification, species pools and more. Deeper understanding of the similarities and differences between island and mainland systems will aid transferability of island theory to continental regions. Main conclusions: As research in biogeography and related fields expands in new directions, islands continue to provide opportunities for developing insights, both as natural laboratories for ecology and evolution and because of the exceptions islands often present to the usual ‘rules’ of ecology. New data collection initiatives are needed on islands world-wide and should be directed towards filling gaps in our knowledge of within-island distributions of species, as well as the functional traits and phylogenetic relationships of island species

Towards a population of HMXB/NS microquasars as counterparts of low-latitude unidentified EGRET sources

The discovery of the microquasar LS 5039 well within the 95% conficence contour of the Unidentified EGRET Source (UES) 3EG J1824-1514 was a major step towards the possible association between microquasars (MQs) and UESs. The recent discovery of precessing relativistic radio jets in LS I +61 303, a source associated for long time with 2CG 135+01 and with the UES 3EG J0241+6103, has given further support to this idea. Finally, the very recently proposed association between the microquasar candidate AX J1639.0-4642 and the UES 3EG J1639-4702 points towards a population of High Mass X-ray Binary (HMXB)/Neutron Star (NS) microquasars as counterparts of low-latitude unidentified EGRET sources.Comment: 12 pages, 7 figures. Proceedings of the Conference "The Multiwavelength Approach to Unidentified Gamma-ray Sources", to appear in the journal Astrophysics and Space Scienc

Klein tunneling in graphene: optics with massless electrons

This article provides a pedagogical review on Klein tunneling in graphene, i.e. the peculiar tunneling properties of two-dimensional massless Dirac electrons. We consider two simple situations in detail: a massless Dirac electron incident either on a potential step or on a potential barrier and use elementary quantum wave mechanics to obtain the transmission probability. We emphasize the connection to related phenomena in optics, such as the Snell-Descartes law of refraction, total internal reflection, Fabry-P\'erot resonances, negative refraction index materials (the so called meta-materials), etc. We also stress that Klein tunneling is not a genuine quantum tunneling effect as it does not necessarily involve passing through a classically forbidden region via evanescent waves. A crucial role in Klein tunneling is played by the conservation of (sublattice) pseudo-spin, which is discussed in detail. A major consequence is the absence of backscattering at normal incidence, of which we give a new shorten proof. The current experimental status is also thoroughly reviewed. The appendix contains the discussion of a one-dimensional toy model that clearly illustrates the difference in Klein tunneling between mono- and bi-layer graphene.Comment: short review article, 18 pages, 14 figures; v3: references added, several figures slightly modifie

Modeling the actinides with disordered local moments

A first-principles disordered local moment (DLM) picture within the local-spin-density and coherent potential approximations (LSDA+CPA) of the actinides is presented. The parameter free theory gives an accurate description of bond lengths and bulk modulus. The case of $\delta$-Pu is studied in particular and the calculated density of states is compared to data from photo-electron spectroscopy. The relation between the DLM description, the dynamical mean field approach and spin-polarized magnetically ordered modeling is discussed.Comment: 6 pages, 4 figure