Search

SPIDER is a balloon-borne instrument designed to map the cosmic microwave background at degree-angular scales in the presence of Galactic foregrounds. SPIDER has mapped a large sky area in the Southern Hemisphere using more than 2000 transition-edge sensors (TESs) during two NASA Long Duration Balloon flights above the Antarctic continent. During its first flight in January 2015, SPIDER observed in the 95 GHz and 150 GHz frequency bands, setting constraints on the B-mode signature of primordial gravitational waves. Its second flight in the 2022-23 season added new receivers at 280 GHz, each using an array of TESs coupled to the sky through feedhorns formed from stacks of silicon wafers. These receivers are optimized to produce deep maps of polarized Galactic dust emission over a large sky area, providing a unique data set with lasting value to the field. In this work, we describe the instrument's performance during SPIDER's second flight., Comment: Submitted to SPIE Astronomical Telescopes + Instrumentation 2024, JATIS

We present the conceptual design of the modular detector and readout system for the Cosmic Microwave Background Stage 4 (CMB-S4) ground-based survey experiment. CMB-S4 will map the cosmic microwave background (CMB) and the millimeter-wave sky to unprecedented sensitivity, using 500,000 superconducting detectors observing from Chile and Antarctica to map over 60 percent of the sky. The fundamental building block of the detector and readout system is a detector module package operated at 100 mK, which is connected to a readout and amplification chain that carries signals out to room temperature. It uses arrays of feedhorn-coupled orthomode transducers (OMT) that collect optical power from the sky onto dc-voltage-biased transition-edge sensor (TES) bolometers. The resulting current signal in the TESs is then amplified by a two-stage cryogenic Superconducting Quantum Interference Device (SQUID) system with a time-division multiplexer to reduce wire count, and matching room-temperature electronics to condition and transmit signals to the data acquisition system. Sensitivity and systematics requirements are being developed for the detector and readout system over a wide range of observing bands (20 to 300 GHz) and optical powers to accomplish CMB-S4's science goals. While the design incorporates the successes of previous generations of CMB instruments, CMB-S4 requires an order of magnitude more detectors than any prior experiment. This requires fabrication of complex superconducting circuits on over 10 square meters of silicon, as well as significant amounts of precision wiring, assembly and cryogenic testing., Comment: 25 pages, 15 figures, presented at and published in the proceedings of SPIE Astronomical Telescopes and Instrumentation 2022

Movement to fully open-access electronic scholarly publication has been hampered by the conflicting interests of universities, private publishers, researchers themselves, and those who fund research. The situation interacts strongly with traditions regarding peer review and the ways in which researchers establish stature within their fields. Progress to date has led to seemingly awkward and probably transient systems of dual publication or dual publication status, including green, gold, and hybrid open access. There are also efforts to establish pay-to-publish as the standard model to replace pay-to-read. The ultimate situation should be immediate open-access electronic posting of results of all research, with pre-posting peer reviews solicited by the author rather than a journal editor, following any institutional policies regarding the type and amount of pre-publication peer review. There could then also be publications and/or web sites that harvest among posted articles selectively for further attention and may be fee-based, but open-access would be the primary and recognized form of publication. There are several things that research universities can do to encourage this transition. One is to provide or arrange for services to facilitate preparation and posting of articles and books in open-access repositories. Another is to make the contents of repositories readily discoverable in searches. The provost should be a central actor toward these ends, since faculty matters, the library, institutional publishing services, and often computing typically report to the provost. A provost can encourage policies for reviews of faculty members that do not consider pre-publication peer reviews and measures of journal quality and which instead give more attention to cumulative and integrated accomplishments than to individual papers. Shared governance provides useful ways of working with the faculty to promote recognition of the value of online, open-access publication. Engaging the interests and support of the most intellectually respected and senior faculty members can be particularly helpful.

A reinterpretation of the complete energy spectrum of the Oxygen-16 nucleus up to 20 MeV, and partly beyond, is proposed. The underlying intrinsic shape of the nucleus is tetrahedral, as in the na\"ive alpha-particle model and other cluster models, and A, E and F vibrational phonons are included. The A- and F-phonons are treated in the harmonic approximation, but the E-vibrations are extended into a two-dimensional E-manifold of D2-symmetric, four-alpha-particle configurations, following earlier work. This allows for the underlying tetrahedral configuration to deform through a square configuration into the dual tetrahedron, so there is tunnelling between the tetrahedron and its dual, with the associated breaking of parity doubling. However, E-manifold states can still be interpreted in terms of E-phonons. Rotational excitations of the vibrational states are analysed as in the classic work of Dennison, Robson and others, with centrifugal corrections to the rotational energy spectrum included. States with F-phonons require Coriolis corrections too. The first-excited $0^+$ state at 6.05 MeV is modelled as a state with two E-phonons; this allows a good fit of the lowest $2^+$ and $2^-$ states as excitations with one E-phonon. The Coriolis parameter $\zeta$ is chosen positive to ensure the right splitting of the $3^+$ and $3^-$ states near 11 MeV. Altogether, about 80 states with isospin zero are predicted below 20 MeV, and these match rather well the more than 60 experimentally tabulated states. Several high-spin states are predicted, up to spin 9 and energy 30 MeV, and these match some of the high-spin, natural parity states in this energy range that have been observed. The model proposed here is mainly phenomenological but it receives some input from analysis of Skyrmions with baryon number 16., Comment: 27 pages, 7 figures. This version accepted for publication in Int. J. Mod. Phys. E

The Gelfand representation of $\mathcal{S}_n$ is the multiplicity-free direct sum of the irreducible representations of $\mathcal{S}_n$. In this paper, we use a result of Adin, Postnikov, and Roichman to find a recursive generating function for the Gelfand character. In order to find this generating function, we investigate descents of so-called $\lambda$-unimodal involutions.

We calculate the low-lying spectrum of the $^{16}$O nucleus using an $\alpha$-cluster model which includes the important tetrahedral and square configurations. Our approach is motivated by the dynamics of $\alpha$-particle scattering in the Skyrme model. We are able to replicate the large energy splitting that is observed between states of identical spin but opposite parities, as well as introduce states that were previously not found in other cluster models, such as a $0^-$ state. We also provide a novel interpretation of the first excited state of $^{16}$O and make predictions for the energies of $6^-$ states that have yet to be observed experimentally., Comment: 5 pages, 9 figures

The scattering of electrons off nuclei is one of the best methods of probing nuclear structure. In this paper we focus on electron scattering off nuclei with spin and isospin zero within the Skyrme model. We consider two distinct methods and simplify our calculations by use of the Born approximation. The first method is to calculate the form factor of the spherically averaged Skyrmion charge density; the second uses the Patterson function to calculate the scattering intensity off randomly oriented Skyrmions, and spherically averages at the end. We compare our findings with experimental scattering data. We also find approximate analytical formulae for the first zero and first stationary point of a form factor., Comment: 24 pages, 38 figures

We investigate the analytic continuation of wave equations into the complex position plane. For the particular case of electromagnetic waves we provide a physical meaning for such an analytic continuation in terms of a family of closely related inhomogeneous media. For bounded permittivity profiles we find the phenomenon of reflection can be related to branch cuts in the wave that originate from poles of the permittivity at complex positions. Demanding that these branch cuts disappear, we derive a large family of inhomogeneous media that are reflectionless for a single angle of incidence. Extending this property to all angles of incidence leads us to a generalized form of the Poschl Teller potentials. We conclude by analyzing our findings within the phase integral (WKB) method., Comment: 18 pages, 8 figures

Most public universities in the United States are formed into systems, containing more than one university or campus. There are clear rationales for these systems, including overall planning and coordination, budgeting efficiency, and effectiveness of dealings with the state government. The distribution of internal governance functions between the system level and the individual-campus level has, however, been a source of continual tension for understandable reasons. Although there can be no hard and fast rules for the division of administrative functions between the system-wide level and the component campuses, a number of governance principles can be laid out. What is done in a particular instance should recognize commonalities and differences in mission among and within systems, the histories and the maturities of the campuses composing the system, state government constraints, governing board structures, and changing conditions, among other circumstances and needs.

Shared governance between the administration and faculty has been traditional for most public universities, but varies considerably in its nature and effectiveness. In the United States it probably takes its most structured form at the University of California. There are good reasons for having shared governance, and yet it tends to be poorly understood outside the university environment and to cause substantial tensions within the university itself. Several trends and issues are identified that pose both significant challenges and substantial opportunities for shared governance. Ways of addressing these and advancing the efficacy of shared governance are put forward and assessed.

From 1972 to 1994, the academic administrative structure of the Berkeley campus of the University of California was unusual, in that it involved two Provosts, one who was also Dean of the College of Letters and Science, and another who was responsible for the remainder of the academic units, which were for the most part professional schools and colleges. The nature of the Provost-Professional Schools and Colleges position is explored, along with some of the issues addressed by the position and the relative advantages and disadvantages of the dual-provost structure. The value of the position stemmed in substantial part from there being common needs and issues among the professional schools, from an ability to give more attention by the campus administration to these schools and to represent their issues within the administration, and from the fact that Berkeley integrates academic planning, program review, and faculty advancement and promotion across all fields, with important roles played by the Academic Senate, which also covers and integrates the entire campus. An analysis is made of the advantages and disadvantages of this structure in comparison with the "each tub on its own bottom" approach that exists more commonly at private institutions.

We present two results about using allele-count (AC) burdens of rare SNPs discovered in a case-control sequencing study for prediction or validation in an external prospective study. When genotyping only the SNPs polymorphic in the sequence data, the phenotype to AC correlation tends to be larger in the replication data than the primary study. Conversely, if the replication sample is sequenced, ACs of SNPs which are novel in the replication tend to have much smaller or opposite signed associations. We explain this by first deriving the AC-phenotype association implied by a model of diverse SNP effects, and second accounting for the shifted distribution of SNP effects when using a case-control study as a filter for SNP inclusion. In rare diseases, the case population is depleted of protective SNPs and enriched for deleterious SNPs, creating the above difference in AC associations. This phenomenon is most relevant in re-sequencing for risk prediction in rare diseases with heterogeneous rare mutations because it applies to SNPs with MAF near 1 out of the case-control sample size and is exaggerated when SNP log-odds ratios come from a heavy-tailed distribution. It also suggests a ``winner's curse'' in which most risk increasing SNPs at a particular MAF are quickly discovered and future sequencing finds more protective or irrelevant SNPs., Comment: Essentially final draft

There is strong interest in broadening engineering education, bringing in more liberal arts content as well as additional subjects such as economics, business and law, with which engineers now have to be familiar. There are also cogent arguments for balancing against what is now the almost exclusively quantitative nature of the curriculum, adding more elements that relate to the actual practice of engineering, and structuring engineering education so as to provide multiple and later entry points, which should enable more informed career choices and make engineering attractive to a more diverse range of the population. Many have also sought a change in the level of the professional engineering degree from the bachelor's to the graduate level, which would logically, and probably also necessarily, accompany these changes. However, progress towards such changes in the United States has been marginal, in large part because incentives on the micro- and meso-scales do not match those on the macro-scale. On the other hand, there is much more substantial change in other countries, driven in part by the Bologna process. For the United States to be the last to change would be counter to the goal of retaining higher-functioning engineering jobs in the U. S. What needs to happen in order for the U. S. to change is evaluated. (Contains 37 endnotes.)

Disciplines codify related knowledge and have developed powerful approaches that enable both solutions to a wide variety of problems and efficient further extension of knowledge. Individual disciplines have translated into individual departments within universities. Academic departments tend to turn inward, deepening the knowledge within the discipline. Because of this inwardness, the differing methodological approaches among disciplines, and the reward systems within disciplines and universities, it is difficult for faculty to reach outside their disciplines and departments, so as to share knowledge and/or mine knowledge at the intersections of disciplines. However, world needs and opportunities are increasingly complex and require integrated, in-depth contributions from multiple disciplines for progress. Means for universities to encourage and facilitate multidisciplinary activities include organizational structure, incentive budgeting, and leadership and resources that enable directors of multidisciplinary units to negotiate effectively with academic department chairs. Major competitive initiatives involving large resources have proven particularly effective. New universities have opportunities for multidisciplinary research and teaching that would be much more difficult within existing universities. Today's university graduates must be able to work effectively with persons from other disciplines and understand enough of the basic vocabulary and methodologies of other disciplines to enable that collaboration. A liberal undergraduate education addresses those needs, where the definition of "liberal" encompasses courses reflecting many different disciplines, including the natural sciences and even some engineering. Professions are properly placed at the graduate level, built upon a foundational liberal education. Engineering should join the other professions by changing to that structure. (Contains 23 endnotes.)

Issues of ethics and leadership are important, growing and intense in universities. Five examples are discussed, drawn from the personal experience of the author. These involve the selection of research, the collection and use of ethically sensitive materials, major relationships with industry and donors, access and admissions, and the content of education itself. Analyses of these cases are couched in terms of some of the major trends affecting public research universities, with one conclusion being that the most challenging situations are those where multiple ethical standards are pertinent, and conflict with one another. (Contains 1 table and 9 notes.)

California has achieved considerable economic success through technological innovation and the formation of businesses based upon those technologies. This paper addresses some of the roles of universities in that success story. It starts with some measures of the contributions of innovation and a robust university structure to the California economy, drawn from the biotechnology and wine industries. This is followed by an exploration of some recent partnership structures involving universities with industry and/or the state government. Emphasis is on the University of California, since that is where the experience of the author lies. This is followed by considerations of how such partnerships can be most successful and at the same time meet concerns about potential undesirable consequences stemming from them. (Contains 38 notes.) [Paper prepared for Salzburg Seminar No. 441, "From Lab to Market: Accelerating Innovation through University, Business, and Government Partnership" (Salzburg, Austria, April 28-May 3, 2007).]

At ICALEPCS '09, we introduced a source code generator that allows processes to communicate safely using data types native to each host language. In this paper, we discuss further development that has occurred since the conference in Kobe, Japan, including the addition of three more client languages, an optimization in network packet size and the addition of a new protocol data type., Comment: 4 pp. 13th International Conference on Accelerator and Large Experimental Physics Control Systems (ICALEPCS 2011). 10-14 Oct 2011. Grenoble, France

The Accelerator Control System at Fermilab has evolved to enable this relatively large control system to be encapsulated into a "box" such as a laptop. The goal was to provide a platform isolated from the "online" control system. This platform can be used internally for making major upgrades and modifications without impacting operations. It also provides a standalone environment for research and development including a turnkey control system for collaborators. Over time, the code base running on Scientific Linux has enabled all the salient features of the Fermilab's control system to be captured in an off-the-shelf laptop. The anticipated additional benefits of packaging the system include improved maintenance, reliability, documentation, and future enhancements., Comment: 3 pp. 13th International Conference on Accelerator and Large Experimental Physics Control Systems (ICALEPCS 2011). 10-14 Oct 2011. Grenoble, France

This study reports on five disciplinary case studies that explore academic value systems as they influence publishing behavior and attitudes of University of California, Berkeley faculty. The case studies are based on direct interviews with relevant stakeholders--faculty, advancement reviewers, librarians, and editors--in five fields: chemical engineering, anthropology, law and economics, English-language literature, and biostatistics. The results of the study strongly confirm the vital role of peer review in faculty attitudes and actual publishing behavior. There is much more experimentation, however, with regard to means of in-progress communication, where single means of publication and communication are not fixed so deeply in values and tradition as they are for final, archival publication. We conclude that approaches that try to "move" faculty and deeply embedded value systems directly toward new forms of archival, "final" publication are destined largely to failure in the short-term. From our perspective, a more promising route is to (1) examine the needs of scholarly researchers for both final and in-progress communications, and (2) determine how those needs are likely to influence future scenarios in a range of disciplinary areas. (Contains 11 notes.)

This paper analyzes the need for providing additional undergraduate enrollment capacity at the University of California (UC) and of alternatives for gaining such capacity at UC and, by extension, other public research universities. In addition to the creation of new campuses, other approaches are capable of giving significant additional capacity as well. Some of these approaches are congruent with academic objectives; others are substantially neutral in that regard; and others probably do lessen the academic experience. A desirable approach is to have new campus sites continually identified, while retaining sufficient capability for alternate means of accommodating enrollment so as to enable continued capacity development in times of budgetary stringency. (Contains 1 figure and 37 footnotes.)

F\"orster's theory of resonant energy transfer (FRET) predicts the strength and range of exciton transport between separated molecules. We introduce an exactly soluble model for FRET which reproduces F\"orster's results as well as incorporating quantum coherence effects. As an application the model is used to analyze a system composed of quantum dots and the protein bacteriorhodopsin., Comment: 10 pages, 2 figures

We present an experimental and theoretical study of magnetocrystalline anisotropies in arrays of bars patterned lithographically into (Ga,Mn)As epilayers grown under compressive lattice strain. Structural properties of the (Ga,Mn)As microbars are investigated by high-resolution X-ray diffraction measurements. The experimental data, showing strong strain relaxation effects, are in good agreement with finite element simulations. SQUID magnetization measurements are performed to study the control of magnetic anisotropy in (Ga,Mn)As by the lithographically induced strain relaxation of the microbars. Microscopic theoretical modeling of the anisotropy is performed based on the mean-field kinetic-exchange model of the ferromagnetic spin-orbit coupled band structure of (Ga,Mn)As. Based on the overall agreement between experimental data and theoretical modeling we conclude that the micropatterning induced anisotropies are of the magnetocrystalline, spin-orbit coupling origin., Comment: 11 pages, 18 figures

We demonstrate a simple, low cost, magneto-transport method for rapidly characterizing the magnetic anisotropy and anisotropic magneto-resistance (AMR) of ferromagnetic devices with uniaxial magnetic anisotropy. This transport technique is the analogue of magnetic susceptibility measurements of bulk material but is applicable to very small samples with low total moment. The technique is used to characterize devices fabricated from the dilute magnetic semiconductor (Ga,Mn)As. The technique allows us to probe the behavior of the parameters close to the Curie temperature, in the limit of the applied magnetic field tending to zero. This avoids the complications arising from the presence of paramagnetism.

We demonstrate dynamic voltage control of the magnetic anisotropy of a (Ga,Mn)As device bonded to a piezoelectric transducer. The application of a uniaxial strain leads to a large reorientation of the magnetic easy axis which is detected by measuring longitudinal and transverse anisotropic magnetoresistance coefficients. Calculations based on the mean-field kinetic-exchange model of (Ga,Mn)As provide microscopic understanding of the measured effect. Electrically induced magnetization switching and detection of unconventional crystalline components of the anisotropic magnetoresistance are presented, illustrating the generic utility of the piezo voltage control to provide new device functionalities and in the research of micromagnetic and magnetotransport phenomena in diluted magnetic semiconductors., Comment: Submitted to Physical Review Letters. Updates version 1 to include a more detailed discussion of the effect of strain on the anisotropic magnetoresistance

We present details of our experimental and theoretical study of the components of the anisotropic magnetoresistance (AMR) in (Ga,Mn)As. We develop experimental methods to yield directly the non-crystalline and crystalline AMR components which are then independently analyzed. These methods are used to explore the unusual phenomenology of the AMR in ultra thin (5nm) (Ga,Mn)As layers and to demonstrate how the components of the AMR can be engineered through lithography induced local lattice relaxations. We expand on our previous [Phys. Rev. Lett. \textbf{99}, 147207 (2007)] theoretical analysis and numerical calculations to present a simplified analytical model for the origin of the non-crystalline AMR. We find that the sign of the non-crystalline AMR is determined by the form of spin-orbit coupling in the host band and by the relative strengths of the non-magnetic and magnetic contributions to the impurity potential., Comment: Submitted to JMMM for conference proceedings of WUN-SPIN 2007 (York, UK)

Our experimental and theoretical study of the non-crystalline and crystalline components of the anisotropic magnetoresistance (AMR) in (Ga,Mn)As is aimed at exploring the basic physical aspects of this relativistic transport effect. The non-crystalline AMR reflects anisotropic lifetimes of the holes due to polarized Mn impurities while the crystalline AMR is associated with valence band warping. We find that the sign of the non-crystalline AMR is determined by the form of spin-orbit coupling in the host band and by the relative strengths of the non-magnetic and magnetic contributions to the impurity potential. We develop experimental methods directly yielding the non-crystalline and crystalline AMR components which are then independently analyzed. We report the observation of an AMR dominated by a large uniaxial crystalline component and show that AMR can be modified by local strain relaxation. We discuss generic implications of our experimental and theoretical findings including predictions for non-crystalline AMR sign reversals in dilute moment systems., Comment: 4 pages, 3 figures. Phys. Rev. Lett. in press

Quantum information theory has generated several interesting conjectures involving products of completely positive maps on matrix algebras, also known as quantum channels. In particular it is conjectured that the output state with maximal p-norm from a product channel is always a product state. It is shown here that the Lieb-Thirring inequality can be used to prove this conjecture for one special case, namely when one of the components of the product channel is of the type known as a diagonal channel, which acts on a state by taking the Hadamard product with a positive matrix., Comment: Presented at ICMP 2003, Lisbon, Portugal

Two measures of sensitivity to eavesdropping for alphabets of quantum states were recently introduced by Fuchs and Sasaki in quant-ph/0302092. These are the accessible fidelity and quantumness. In this paper we prove an important property of both measures: They are multiplicative under tensor products. The proof in the case of accessible fidelity shows a connection between the measure and characteristics of entanglement-breaking quantum channels.

This paper derives an inequality relating the p-norm of a positive 2 x 2 block matrix to the p-norm of the 2 x 2 matrix obtained by replacing each block by its p-norm. The inequality had been known for integer values of p, so the main contribution here is the extension to all values p >= 1. In a special case the result reproduces Hanner's inequality. As an application in quantum information theory, the inequality is used to obtain some results concerning maximal p-norms of product channels.

It shown that when one of the components of a product channel is entanglement breaking, the output state with maximal p-norm is always a product state. This result complements Shor's theorem that both minimal entropy and Holevo capacity are additive for entanglement breaking channels. It is also shown how Shor's results can be recovered from the p-norm results by considering their behavior for p close to one., Comment: 7 pages

The information carrying capacity of the d-dimensional depolarizing channel is computed. It is shown that this capacity can be achieved by encoding messages as products of pure states belonging to an orthonormal basis of the state space, and using measurements which are products of projections onto this same orthonormal basis. In other words, neither entangled signal states nor entangled measurements give any advantage for information capacity. The result follows from an additivity theorem for the capacity of the product of the depolarizing channel with an arbitrary channel. We establish the Amosov-Holevo-Werner p-norm conjecture for this product channel for all p >= 1, and deduce from this the additivity of the minimal entropy and of the Holevo quantity., Comment: 25 pages, no figures; error in earlier version corrected; discussion of qubit depolarizing channel added

Additivity of the Holevo capacity is proved for product channels, under the condition that one of the channels is in a certain class of unital qubit channels, with the other completely arbitrary. This qubit class includes the depolarizing channel. As a byproduct this proves that the Holevo bound is the ultimate information capacity of such qubit channels (assuming no prior entanglement between sender and receiver). Additivity of minimal entropy and multiplicativity of p-norms are also proved under the same assumptions.

It is conjectured that the Holevo capacity of a product channel \Omega \otimes \Phi is achieved when product states are used as input. Amosov, Holevo and Werner have also conjectured that the maximal p-norm of a product channel is achieved with product input states. In this paper we establish both of these conjectures in the case that \Omega is arbitrary and \Phi is a CQ or QC channel (as defined by Holevo). We also establish the Amosov, Holevo and Werner conjecture when \Omega is arbitrary and either \Phi is a qubit channel and p=2, or \Phi is a unital qubit channel and p is integer. Our proofs involve a new conjecture for the norm of an output state of the half-noisy channel I \otimes \Phi, when \Phi is a qubit channel. We show that this conjecture in some cases also implies additivity of the Holevo capacity.

We introduce a new method to generate duality relations for correlation functions of the Potts model on planar graphs. The method extends previously known results, by allowing the consideration of the correlation function for arbitrarily placed vertices on the graph. We show that generally it is linear combinations of correlation functions, not the individual correlations, that are related by dualities. The method is illustrated in several non-trivial cases, and the relation to earlier results is explained. A graph-theoretical formulation of our results in terms of rooted dichromatic, or Tutte, polynomials is also given.

The capacity of a quantum channel for transmission of classical information depends in principle on whether product states or entangled states are used at the input, and whether product or entangled measurements are used at the output. We show that when product measurements are used, the capacity of the channel is achieved with product input states, so that entangled inputs do not increase capacity. We show that this result continues to hold if sequential measurements are allowed, whereby the choice of successive measurements may depend on the results of previous measurements. We also present a new simplified expression which gives an upper bound for the Shannon capacity of a channel, and which bears a striking resemblance to the well-known Holevo bound., Comment: Revision with minor corrections and expanded discussion clarifying several points. latex, 19 pages

In this paper, we consider the minimal entropy of qubit states transmitted through two uses of a noisy quantum channel, which is modeled by the action of a completely positive trace-preserving (or stochastic) map. We provide strong support for the conjecture that this minimal entropy is additive, namely that the minimum entropy can be achieved when product states are transmitted. Explicitly, we prove that for a tensor product of two unital stochastic maps on qubit states, using an entanglement that involves only states which emerge with minimal entropy cannot decrease the entropy below the minimum achievable using product states. We give a separate argument, based on the geometry of the image of the set of density matrices under stochastic maps, which suggests that the minimal entropy conjecture holds for non-unital as well as for unital maps. We also show that the maximal norm of the output states is multiplicative for most product maps on $n$-qubit states, including all those for which at least one map is unital. For the class of {\it unital} channels on ${\bf C}^2$, we show that additivity of minimal entropy implies that the Holevo capacity of the channel is {\it additive} over two inputs, achievable with orthogonal states, and equal to the Shannon capacity. This implies that superadditivity of the capacity is possible only for non-unital channels., Comment: LATEX file; 44 pages, 7 figures; references added, typos corrected; extended discussion of additivity for minimal entropy vs capacity

The Tutte polynomial is a generalization of the chromatic polynomial of graph colorings. Here we present an extension called the rooted Tutte polynomial, which is defined on a graph where one or more vertices are colored with prescribed colors. We establish a number of results pertaining to the rooted Tutte polynomial, including a duality relation in the case that all roots reside around a single face of a planar graph. The connection with the Potts model is also reviewed., Comment: plain latex, 14 pages, 2 figs., to appear in Annales de l'Institut Fourier (1999)

A new link invariant is derived using the exactly solvable chiral Potts model and a generalized Gaussian summation identity. Starting from a general formulation of link invariants using edge-interaction spin models, we establish the uniqueness of the invariant for self-dual models. We next apply the formulation to the self-dual chiral Potts model, and obtain a link invariant in the form of a lattice sum defined by a matrix associated with the link diagram. A generalized Gaussian summation identity is then used to carry out this lattice sum, enabling us to cast the invariant into a tractable form. The resulting expression for the link invariant is characterized by roots of unity and does not appear to belong to the usual quantum group family of invariants. A table of invariants for links with up to 8 crossings is given., Comment: 32 pages + 9 figures

A study was undertaken at the request of the Orem (Utah) Public Library administration to identify the library's strengths and weaknesses, and to measure how close they were to achieving their target goal of 100% effectiveness in the areas of referral, accuracy, and consistency, in order to improve the quality of reference services. Data were collected using unobtrusive measures. Proxy library users posed each ready reference and referral question to three different reference librarians to check for consistency. Of the full- and part-time librarians at Orem, one had a Masters of Library Science degree, one had a Masters of English, five had four-year bachelors degrees, and one had an associate degree. The questions were asked over the course of 15 days so that each librarian would be asked at least two ready reference questions and two referral questions. The library achieved an overall accuracy rate of 59.2%, which corresponds closely with rates reported in similar studies. Comments and observations from proxies suggest that a lack of awareness may exist among reference librarians as to the information contained in the reference collection, and it is suggested that librarians may benefit from regular in-house training to increase their familiarity with the reference collection and outside sources. (17 references) (SD)

Currently there are several hypotheses for the thermal state of the early Earth. Some hypothesize a shallow magma ocean, or deep magma ocean, or heterogeneous accretion which requires no magma ocean at all. Previous models are unable to account for Ge depletion in Earth's mantle relative to CI chondrites. In this study, the element Ge is used to observe the way siderophile elements partition into the metallic core. The purpose of this research is to provide new data for Ge and to further test these models for Earth's early stages. The partition coefficients (D(sub Ge) = c(sub metal)/c(sub silicate), where D = partition coefficient of Ge and c = concentration of Ge in the metal and silicate, respectively) of siderophile elements were studied by performing series of high pressure, high temperature experiments. They are also dependent on oxygen fugacity, and metal and silicate composition. Ge is a moderately siderophile element found in both the mantle and core, and has yet to be studied systematically at high temperatures. Moreover, previous work has been limited by the low solubility of Ge in silicate melts (less than 100 ppm and close to detection limits for electron microprobe analysis). Reported here are results from 14 experiments studying the partitioning of Ge between silicate and metallic liquids. The Ge concentrations were then analyzed using Laser Ablation Inductively Coupled Mass Spectrometry (LA-ICP-MS) which is sensitive enough to detect ppm levels of Ge in the silicate melt.

The design philosophy that will guide the design of early lunar habitats will be based on a compromise between the desired capabilities of the base and the economics of its development and implantation. Preferred design will be simple, make use of existing technologies, require the least amount of lunar surface preparation, and minimize crew activity. Three concepts for an initial habitat supporting a crew of four for 28 to 30 days are proposed. Two of these are based on using Space Station Freedom structural elements modified for use in a lunar-gravity environment. A third concept is proposed that is based on an earlier technology based on expandable modules. The expandable modules offer significant advantages in launch mass and packaged volume reductions. It appears feasible to design a transport spacecraft lander that, once landed, can serve as a habitat and a stand-off for supporting a regolith environmental shield. A permanent lunar base habitat supporting a crew of twelve for an indefinite period can be evolved by using multiple initial habitats. There appears to be no compelling need for an entirely different structure of larger volume and increased complexity of implantation.