Deceptive signals of phase transitions in small magnetic clusters

We present an analysis of the thermodynamic properties of small transition metal clusters and show how the commonly used indicators of phase transitions like peaks in the specific heat or magnetic susceptibility can lead to deceptive interpretations of the underlying physics. The analysis of the distribution of zeros of the canonical partition function in the whole complex temperature plane reveals the nature of the transition. We show that signals in the magnetic susceptibility at positive temperatures have their origin at zeros lying at negative temperatures.Comment: 4 pages, 5 figures, revtex4, for further information see http://www.smallsystems.d

Advances to ASHRAE Standard 55 to encourage more effective building practice

ASHRAE Standard 55 has been evolving in recent years to encourage more sustainable building designs and operational practices. A series of changes address issues for which past design practice has been deficient or overly constrained. Some of the changes were enabled by findings from field studies of comfort and energy-efficiency, and others by new developments in the design- and building-management professions.  The changes have been influencing practice and spurring follow-on research.The Standard now addresses effects of elevated air movement, solar gain on the occupant, and draft at the ankles, each with several impacts on energy-efficient design and operation. It also addresses the most important source of discomfort in modern buildings, the large inter- and intra-personal variability in thermal comfort requirements, by classifying the occupants’ personal control and adaptive options in a form that can be used in building rating systems. In order to facilitate design, new computer tools extend the use of the standard toward direct use in designers’ workflow. The standard also includes provisions for monitoring and evaluating buildings in operation. This paper summarizes these developments and their underlying research, and attempts to look ahead

Review: Effect of global warming on plant evolution and diversity; lessons from the past and its potential recurrence in the future

Abstrak. Setyawan AD. 2009. Pengaruh pemanasan global terhadap evolusi dan keanekaragaman tumbuhan; pelajaran dari masa lalu dan kemungkinan terulangnya kembali di masa depan. Nusantara Bioscience 1: 43-52. Pelajaran dari masa lalu menunjukkan bahwa pemanasan global dan glasiasi merupakan siklus alamiah yang terus berulang; faktor pemicunya tidak selalu sama, namun pemanasan global selalu disertai peningkatan kadar CO2 dan gas-gas rumah kaca lainnya di atmosfer yang menyebabkan meningkatnya suhu bumi. Hadir dan musnahnya berbagai tumbuhan dan makhluh hidup lainnya terus terjadi dari waktu ke waktu. Setiap jaman memiliki bentuk kehidupannya sendiri-sendiri, sebagai cermin kondisi lingkungan global pada saat itu. Keanekaragaman hayati tidak selalu sama antara masa pemanasan global yang satu dengan masa pemanasan global berikutnya; atau dari masa glasiasi yang satu dengan glasiasi berikutnya, meskipun keturunan-keturunan baru selalu menunjukkan jejak evolusi dari nenek moyangnya. Manusia merupakan salah satu agen pemanasan global yang dimulai dengan dikembangkannya sistem pertanian sejak 8000 tahun yang lalu. Dampak perubahan iklim akibat pemanasan global perlu terus diwaspadai. Berdasarkan pengalaman di masa lalu, pemanasan global selalu diikuti kepunahan massal, namun berbagai bentuk kehidupan tetap akan bertahan meskipun bentuknya hampir pasti tidak sama dengan yang ada sebelumnya. Makhluk hidup yang dapat bertahan akan berevolusi menjadi taksa baru yang berbeda dengan taksa tetuanya. Manusia yang hadir pada saat itu barangkali bukanlah manusia yang hadir saat ini, mengingat boleh jadi Homo sapiens telah punah karena tidak mampu beradaptasi atau sebaliknya telah berevolusi menjadi manusia baru yang barangkali tidak lagi menunjukkan ciri-ciri manusia bijaksana. Kata kunci: pemanasan global, evolusi, keanekaragaman, jenis baru

R-symmetry and Supersymmetry Breaking at Finite Temperature

We analyze the spontaneous $U(1)_R$ symmetry breaking at finite temperature for the simple O'Raifeartaigh-type model introduced in [1] in connection with spontaneous supersymmetry breaking. We calculate the finite temperature effective potential (free energy) to one loop order and study the thermal evolution of the model. We find that the R-symmetry breaking occurs through a second order phase transition. Its associated meta-stable supersymmetry breaking vacuum is thermodynamically favored at high temperatures and the model remains trapped in this state by a potential barrier, as the temperature lowers all the way until T=0.Comment: 19 pages, 4 figures - Minor revisions, references added. To appear in JHE

The JCMT Gould Belt Survey: Evidence for radiative heating in Serpens MWC 297 and its influence on local star formation

We present SCUBA-2 450micron and 850micron observations of the Serpens MWC 297 region, part of the JCMT Gould Belt Survey of nearby star-forming regions. Simulations suggest that radiative feedback influences the star-formation process and we investigate observational evidence for this by constructing temperature maps. Maps are derived from the ratio of SCUBA-2 fluxes and a two component model of the JCMT beam for a fixed dust opacity spectral index of beta = 1.8. Within 40 of the B1.5Ve Herbig star MWC 297, the submillimetre fluxes are contaminated by free-free emission with a spectral index of 1.03+-0.02, consistent with an ultra-compact HII region and polar winds/jets. Contamination accounts for 73+-5 per cent and 82+-4 per cent of peak flux at 450micron and 850micron respectively. The residual thermal disk of the star is almost undetectable at these wavelengths. Young Stellar Objects are confirmed where SCUBA-2 850micron clumps identified by the fellwalker algorithm coincide with Spitzer Gould Belt Survey detections. We identify 23 objects and use Tbol to classify nine YSOs with masses 0.09 to 5.1 Msun. We find two Class 0, one Class 0/I, three Class I and three Class II sources. The mean temperature is 15+-2K for the nine YSOs and 32+-4K for the 14 starless clumps. We observe a starless clump with an abnormally high mean temperature of 46+-2K and conclude that it is radiatively heated by the star MWC 297. Jeans stability provides evidence that radiative heating by the star MWC 297 may be suppressing clump collapse.Comment: 24 pages, 13 figures, 7 table

Orbital order in classical models of transition-metal compounds

We study the classical 120-degree and related orbital models. These are the classical limits of quantum models which describe the interactions among orbitals of transition-metal compounds. We demonstrate that at low temperatures these models exhibit a long-range order which arises via an "order by disorder" mechanism. This strongly indicates that there is orbital ordering in the quantum version of these models, notwithstanding recent rigorous results on the absence of spin order in these systems.Comment: 7 pages, 1 eps fi

NEW TOPOLOGIES IN THE PHASE DIAGRAM OF THE SEMI-INFINITE BLUME-CAPEL MODEL

The phase diagram of the Blume--Capel model on a semi--infinite simple cubic lattice with a (100) free surface is studied in the pair approximation of the cluster variation method. Six main topologies are found, of which two are new, due to the occurrence of a first order surface transition in the phase with ordered bulk, separating two phases with large and small surface order parameters. The latter is a new phase and is studied in some detail, giving the behaviour of the order parameter profiles in two typical cases. A comparison is made with the results of a low temperature expansion, where these are available, showing a great increase in accuracy with respect to the mean field approximation.Comment: RevTeX, 13 pages + 7 uuencoded PostScript figures (substituted raw with encoded PostScript

Phases and phase transitions in disordered quantum systems

These lecture notes give a pedagogical introduction to phase transitions in disordered quantum systems and to the exotic Griffiths phases induced in their vicinity. We first review some fundamental concepts in the physics of phase transitions. We then derive criteria governing under what conditions spatial disorder or randomness can change the properties of a phase transition. After introducing the strong-disorder renormalization group method, we discuss in detail some of the exotic phenomena arising at phase transitions in disordered quantum systems. These include infinite-randomness criticality, rare regions and quantum Griffiths singularities, as well as the smearing of phase transitions. We also present a number of experimental examples.Comment: Pedagogical introduction to strong disorder physics at quantum phase transitions. Based on lectures given at the XVII Training Course in the Physics of Strongly Correlated Systems in Vietri sul Mare, Italy in October 2012. Submitted to the proceedings of this school. 60 pages and 23 figures. Builds on material reviewed in arXiv:cond-mat/0602312 and arXiv:1005.270