Minimal conditions for the creation of a Friedman-Robertson-Walker universe from a "bounce"

We investigate the minimal conditions under which the creation of our universe might arise due to a "bounce" from a previous collapse, rather than an explosion from a big-bang singularity. Such a bounce is sometimes referred to as a Tolman wormhole. We subject the bounce to a general model-independent analysis along the lines of that applied to the Morris-Thorne traversable wormholes, and show that there is always an open temporal region surrounding the bounce over which the strong energy condition (SEC) must be violated. On the other hand, all the other energy conditions can easily be satisfied. In particular, we exhibit an inflation-inspired model in which a big bounce is "natural".Comment: 4 pages, ReV-TeX 3.

Ariel - Volume 12(13) Number 4

Co-Editors Gary Fishbein Lynn Solomon Business Manager Rich Davis Assistant Business Manager Jeff Lavanier Layout Editors Paul J. Berlin Tracy A. Glauser Photography Editor Ben Alma

The importance of cross-validation, accuracy, and precision for measuring plumage color: A comment on Vaquero-Alba et al. (2016)

Vaquero-Alba and colleagues published a study in The Auk: Ornithological Advances comparing objective color measurements of plumage taken in the field directly on a bird’s body to those taken in the lab on collected feathers arranged to emulate the appearance of a bird’s natural plumage. Although the field measures of plumage color were less repeatable than lab measures, the authors concluded that measurements taken in the field were more representative of a bird’s ‘‘true color.’’ Accordingly, they recommend that researchers should bring spectrophotometers into the field to measure color on live birds. We question the assumption that their field measurements represent true color and highlight concerns regarding their experimental design and methodology. Because they did not measure color of live birds in the lab or the color of plucked feathers in the field, they cannot directly test whether the assessment of color in the field on a live bird is superior. Also, rather than assume field measures are the most accurate or precise way to assess plumage color, we suggest cross-validation with other methodologies, such as digital photography, pigment biochemistry, or measures of a known color standard in both environments. Importantly, researchers should be aware of the limitations and advantages of various methods for measuring plumage color so they can use the method most appropriate for their study. Vaquero-Alba y sus colaboradores publicaron un estudio en The Auk comparando medidas objetivas del color del plumaje tomadas en el campo directamente en el cuerpo del ave con medidas tomadas en el laboratorio en plumas recolectadas y organizadas para emular la apariencia natural del plumaje. Aunque las medidas de campo del color del plumaje fueron menos repetibles que las de laboratorio, los autores concluyeron que las medidas tomadas en el campo fueron ma´s representativas del ‘‘color verdadero’’ de un ave. En consecuencia, recomendaron que los investigadores deben llevar espectrofot ´ ometros a los sitios de campo para medir el color en aves vivas. Cuestionamos la suposici ´on de que sus mediciones de campo representan el ‘‘color verdadero’’ y resaltamos nuestras preocupaciones con respecto a su dise ˜no experimental y metodolog´ıa. Debido a que ellos no midieron el color de las aves vivas en el laboratorio ni el color de las plumas sueltas en el campo, no pueden evaluar directamente si la evaluaci ´on del color en el campo en un ave viva es superior. Tambi´en, en vez de asumir que las medidas de campo son la forma ma´s exacta o precisa de determinar el color del plumaje, sugerimos que se haga una validaci ´on cruzada con otras metodolog´ıas como la fotograf´ıa digital, la bioqu´ımica de los pigmentos o las medidas de un esta´ndar de un color conocido en ambos ambientes. Es importante que los investigadores tengan en cuenta las limitaciones y avances en varios m´etodos para medir el color del plumaje para que puedan usar el m´etodo ma´s apropiado para su estudio

The importance of cross-validation, accuracy, and precision for measuring plumage color: A comment on Vaquero-Alba et al. (2016)

Vaquero-Alba and colleagues published a study in The Auk: Ornithological Advances comparing objective color measurements of plumage taken in the field directly on a bird’s body to those taken in the lab on collected feathers arranged to emulate the appearance of a bird’s natural plumage. Although the field measures of plumage color were less repeatable than lab measures, the authors concluded that measurements taken in the field were more representative of a bird’s ‘‘true color.’’ Accordingly, they recommend that researchers should bring spectrophotometers into the field to measure color on live birds. We question the assumption that their field measurements represent true color and highlight concerns regarding their experimental design and methodology. Because they did not measure color of live birds in the lab or the color of plucked feathers in the field, they cannot directly test whether the assessment of color in the field on a live bird is superior. Also, rather than assume field measures are the most accurate or precise way to assess plumage color, we suggest cross-validation with other methodologies, such as digital photography, pigment biochemistry, or measures of a known color standard in both environments. Importantly, researchers should be aware of the limitations and advantages of various methods for measuring plumage color so they can use the method most appropriate for their study. Vaquero-Alba y sus colaboradores publicaron un estudio en The Auk comparando medidas objetivas del color del plumaje tomadas en el campo directamente en el cuerpo del ave con medidas tomadas en el laboratorio en plumas recolectadas y organizadas para emular la apariencia natural del plumaje. Aunque las medidas de campo del color del plumaje fueron menos repetibles que las de laboratorio, los autores concluyeron que las medidas tomadas en el campo fueron ma´s representativas del ‘‘color verdadero’’ de un ave. En consecuencia, recomendaron que los investigadores deben llevar espectrofot ´ ometros a los sitios de campo para medir el color en aves vivas. Cuestionamos la suposici ´on de que sus mediciones de campo representan el ‘‘color verdadero’’ y resaltamos nuestras preocupaciones con respecto a su dise ˜no experimental y metodolog´ıa. Debido a que ellos no midieron el color de las aves vivas en el laboratorio ni el color de las plumas sueltas en el campo, no pueden evaluar directamente si la evaluaci ´on del color en el campo en un ave viva es superior. Tambi´en, en vez de asumir que las medidas de campo son la forma ma´s exacta o precisa de determinar el color del plumaje, sugerimos que se haga una validaci ´on cruzada con otras metodolog´ıas como la fotograf´ıa digital, la bioqu´ımica de los pigmentos o las medidas de un esta´ndar de un color conocido en ambos ambientes. Es importante que los investigadores tengan en cuenta las limitaciones y avances en varios m´etodos para medir el color del plumaje para que puedan usar el m´etodo ma´s apropiado para su estudio

Different Lines of Rats Selectively-Bred for High Alcohol-Drinking Demonstrate Disparate Preferences for Nicotine Self-administration

Background. Alcohol and nicotine are commonly co-abused. The search for a common core of neural, behavioral, and genetic factors underlying addiction has been the goal of addiction research. Purpose. Genetic predisposition to high alcohol intake has been studied in rats by selectively breeding rats that have high preference for alcohol. The current experiments were conducted to determine if the level of intravenous nicotine administration for the various lines of alcohol-preferring rats differs from that for nonalcohol-preferring controls. Study design. Adult alcohol-naïve selectively-bred alcohol-preferring male rats from four lines (P, AA, HAD-1, sP) and their control nonalcohol-preferring rats (NP, ANA, LAD-1, sNP) were trained and given access to self-administer nicotine (0.03 mg/kg/infusion). Results. The results show that the P rats self-administered significantly more nicotine than NP rats. In contrast, there were no significant differences in nicotine self-administration between the sP and sNP or the AA and ANA rats. Unexpectedly, high alcohol-drinking HAD-1 rats self-administered significantly less nicotine than low alcohol-drinking LAD-1 rats. Conclusion. This suggests that some genetic factors that underlie high-alcohol intake have more general effects in promoting high nicotine intake tendencies, while other genetic factors are more specific to only heavy drinking

Geometrodynamics of Variable-Speed-of-Light Cosmologies

This paper is dedicated to the memory of Dennis Sciama. Variable-Speed-of-Light (VSL) cosmologies are currently attracting interest as an alternative to inflation. We investigate the fundamental geometrodynamic aspects of VSL cosmologies and provide several implementations which do not explicitly break Lorentz invariance (no "hard" breaking). These "soft" implementations of Lorentz symmetry breaking provide particularly clean answers to the question "VSL with respect to what?". The class of VSL cosmologies we consider are compatible with both classical Einstein gravity and low-energy particle physics. These models solve the "kinematic" puzzles of cosmology as well as inflation does, but cannot by themselves solve the flatness problem, since in their purest form no violation of the strong energy condition occurs. We also consider a heterotic model (VSL plus inflation) which provides a number of observational implications for the low-redshift universe if chi contributes to the "dark energy" either as CDM or quintessence. These implications include modified gravitational lensing, birefringence, variation of fundamental constants and rotation of the plane of polarization of light from distant sources.Comment: 19 pages, latex 209, revtex 3.1; To appear in Physical Review D; Numerous small changes of presentation and emphasis; new section on the entropy problem; references updated; central results unaffecte

Gravitating discs around black holes

Fluid discs and tori around black holes are discussed within different approaches and with the emphasis on the role of disc gravity. First reviewed are the prospects of investigating the gravitational field of a black hole--disc system by analytical solutions of stationary, axially symmetric Einstein's equations. Then, more detailed considerations are focused to middle and outer parts of extended disc-like configurations where relativistic effects are small and the Newtonian description is adequate. Within general relativity, only a static case has been analysed in detail. Results are often very inspiring, however, simplifying assumptions must be imposed: ad hoc profiles of the disc density are commonly assumed and the effects of frame-dragging and completely lacking. Astrophysical discs (e.g. accretion discs in active galactic nuclei) typically extend far beyond the relativistic domain and are fairly diluted. However, self-gravity is still essential for their structure and evolution, as well as for their radiation emission and the impact on the environment around. For example, a nuclear star cluster in a galactic centre may bear various imprints of mutual star--disc interactions, which can be recognised in observational properties, such as the relation between the central mass and stellar velocity dispersion.Comment: Accepted for publication in CQG; high-resolution figures will be available from http://www.iop.org/EJ/journal/CQ

Asc1 Supports Cell-Wall Integrity Near Bud Sites by a Pkc1 Independent Mechanism

Background: The yeast ribosomal protein Asc1 is a WD-protein family member. Its mammalian ortholog, RACK1 was initially discovered as a receptor for activated protein C kinase (PKC) that functions to maintain the active conformation of PKC and to support its movement to target sites. In the budding yeast though, a connection between Asc1p and the PKC signaling pathway has never been reported. Methodology/Principal Findings: In the present study we found that asc1-deletion mutant (asc1D) presents some of the hallmarks of PKC signaling mutants. These include an increased sensitivity to staurosporine, a specific Pkc1p inhibitor, and susceptibility to cell-wall perturbing treatments such as hypotonic- and heat shock conditions and zymolase treatment. Microscopic analysis of asc1D cells revealed cell-wall invaginations near bud sites after exposure to hypotonic conditions, and the dynamic of cells ’ survival after this stress further supports the involvement of Asc1p in maintaining the cell-wall integrity during the mid-to late stages of bud formation. Genetic interactions between asc1 and pkc1 reveal synergistic sensitivities of a double-knock out mutant (asc1D/pkc1D) to cell-wall stress conditions, and high basal level of PKC signaling in asc1D. Furthermore, Asc1p has no effect on the cellular distribution or redistribution of Pkc1p at optimal or at cell-wall stress conditions. Conclusions/Significance: Taken together, our data support the idea that unlike its mammalian orthologs, Asc1p act

The predictive value of highly malignant EEG patterns after cardiac arrest: evaluation of the ERC-ESICM recommendations

Purpose: The 2021 guidelines endorsed by the European Resuscitation Council (ERC) and the European Society of Intensive Care Medicine (ESICM) recommend using highly malignant electroencephalogram (EEG) patterns (HMEP; suppression or burst-suppression) at > 24 h after cardiac arrest (CA) in combination with at least one other concordant predictor to prognosticate poor neurological outcome. We evaluated the prognostic accuracy of HMEP in a large multicentre cohort and investigated the added value of absent EEG reactivity. Methods: This is a pre-planned prognostic substudy of the Targeted Temperature Management trial 2. The presence of HMEP and background reactivity to external stimuli on EEG recorded > 24 h after CA was prospectively reported. Poor outcome was measured at 6 months and defined as a modified Rankin Scale score of 4-6. Prognostication was multimodal, and withdrawal of life-sustaining therapy (WLST) was not allowed before 96 h after CA. Results: 845 patients at 59 sites were included. Of these, 579 (69%) had poor outcome, including 304 (36%) with WLST due to poor neurological prognosis. EEG was recorded at a median of 71 h (interquartile range [IQR] 52-93) after CA. HMEP at > 24 h from CA had 50% [95% confidence interval [CI] 46-54] sensitivity and 93% [90-96] specificity to predict poor outcome. Specificity was similar (93%) in 541 patients without WLST. When HMEP were unreactive, specificity improved to 97% [94-99] (p = 0.008). Conclusion: The specificity of the ERC-ESICM-recommended EEG patterns for predicting poor outcome after CA exceeds 90% but is lower than in previous studies, suggesting that large-scale implementation may reduce their accuracy. Combining HMEP with an unreactive EEG background significantly improved specificity. As in other prognostication studies, a self-fulfilling prophecy bias may have contributed to observed results