Showing 721 - 730 of 2039 Items
Clarifying (Opportunity) Costs
Date: 2015-05-01
Creator: Daniel F. Stone
Access: Open access
- Opportunity cost is widely considered to be a fundamental concept in economics. But the definition of the term continues to be both unclear and controversial. I describe how the term is widely used in two distinct ways, both in academic and non-academic contexts. I propose a practical way for educators to clarify the concept and related terminology.
Investigating the Role of Interpretation Bias in Mindfulness-Based Treatment of Adults With Generalized Anxiety Disorder
Date: 2020-02-11
Creator: Elizabeth A. Hoge
Hannah E. Reese
Isabelle A. Oliva
Caroline D. Gabriel
Brittany M., Guidos
Eric Bui
Naomi M. Simon
Mary Ann Dutton
Access: Open access
- Although mindfulness-based interventions (MBIs) have garnered empirical support for a wide range of psychological conditions, the psychological processes that mediate the relationship between MBIs and subsequent symptomatic improvement are less well-understood. In the present study we sought to examine, for the first time, the relationship between mindfulness, negative interpretation bias as measured by the homophone task, and anxiety among adults with Generalized Anxiety Disorder (GAD). Forty-two individuals with GAD completed measures of mindfulness, interpretation bias, and anxiety before and after treatment with Mindfulness-based Stress Reduction (MBSR). Contrary to prior research, we did not find evidence of an indirect relationship between baseline levels of mindfulness and anxiety via negative interpretation bias. MBSR did result in significant reductions in negative interpretation bias from baseline to post-treatment; however, we did not find evidence of an indirect relationship between changes in mindfulness and changes in anxiety via changes in interpretation bias. Taken together, these results provide minimal support for the hypothesized relationship between mindfulness, negative interpretation bias, and anxiety among adults with GAD. Limitations and specific suggestions for further inquiry are discussed.
Haplotype mapping of a diploid non-meiotic organism using existing and induced aneuploidies
Date: 2008-01-01
Creator: Melanie Legrand
Anja Forche
Anna Selmecki
Christine Chan
David T., Kirkpatrick
Judith Berman
Access: Open access
- Haplotype maps (HapMaps) reveal underlying sequence variation and facilitate the study of recombination and genetic diversity. In general, HapMaps are produced by analysis of Single-Nucleotide Polymorphism (SNP) segregation in large numbers of meiotic progeny. Candida albicans, the most common human fungal pathogen, is an obligate diploid that does not appear to undergo meiosis. Thus, standard methods for haplotype mapping cannot be used. We exploited naturally occurring aneuploid strains to determine the haplotypes of the eight chromosome pairs in the C. albicans laboratory strain SC5314 and in a clinical isolate. Comparison of the maps revealed that the clinical strain had undergone a significant amount of genome rearrangement, consisting primarily of crossover or gene conversion recombination events. SNP map haplotyping revealed that insertion and activation of the UAU1 cassette in essential and non-essential genes can result in whole chromosome aneuploidy. UAU1 is often used to construct homozygous deletions of targeted genes in C. albicans; the exact mechanism (trisomy followed by chromosome loss versus gene conversion) has not been determined. UAU1 insertion into the essential ORC1 gene resulted in a large proportion of trisomic strains, while gene conversion events predominated when UAU1 was inserted into the non-essential LRO1 gene. Therefore, induced aneuploidies can be used to generate HapMaps, which are essential for analyzing genome alterations and mitotic recombination events in this clonal organism. © 2008 Legrand et al.
Expert assessment of vulnerability of permafrost carbon to climate change
Date: 2013-07-01
Creator: E. A.G. Schuur
B. W. Abbott
W. B. Bowden
V. Brovkin
P., Camill
J. G. Canadell
J. P. Chanton
F. S. Chapin
T. R. Christensen
P. Ciais
B. T. Crosby
C. I. Czimczik
G. Grosse
J. Harden
D. J. Hayes
G. Hugelius
Access: Open access
- Approximately 1700 Pg of soil carbon (C) are stored in the northern circumpolar permafrost zone, more than twice as much C than in the atmosphere. The overall amount, rate, and form of C released to the atmosphere in a warmer world will influence the strength of the permafrost C feedback to climate change. We used a survey to quantify variability in the perception of the vulnerability of permafrost C to climate change. Experts were asked to provide quantitative estimates of permafrost change in response to four scenarios of warming. For the highest warming scenario (RCP 8.5), experts hypothesized that C release from permafrost zone soils could be 19-45 Pg C by 2040, 162-288 Pg C by 2100, and 381-616 Pg C by 2300 in CO equivalent using 100-year CH global warming potential (GWP). These values become 50 % larger using 20-year CH GWP, with a third to a half of expected climate forcing coming from CH even though CH was only 2.3 % of the expected C release. Experts projected that two-thirds of this release could be avoided under the lowest warming scenario (RCP 2.6). These results highlight the potential risk from permafrost thaw and serve to frame a hypothesis about the magnitude of this feedback to climate change. However, the level of emissions proposed here are unlikely to overshadow the impact of fossil fuel burning, which will continue to be the main source of C emissions and climate forcing. © 2013 The Author(s). 2 4 4 4 4
Spending Fast and Furious: Political Advertising in 2020
Date: 2021-03-01
Creator: Travis N. Ridout
Erika Franklin Fowler
Michael M. Franz
Access: Open access
- This article is a "first look"at political advertising in 2020. Spending on political advertising in the United States in 2020 obliterated records, and Democrats held huge advantages in the presidential race and in most congressional and senatorial races. In addition, all indicators suggest that spending on digital advertising continued to rise. Political advertising was largely similar in tone to past years and, in the presidential race, was substantially more positive than 2016. In addition, interest groups remained heavily involved in federal races in 2020, airing more ads than ever before, though their spending as a percentage of total ad spending was slightly less than in 2016. Political ad spending in 2020 may have been historically high because of the impact of COVID-19 on how campaigns could reach voters, suggesting that paid advertising may decline in 2022 and 2024, at least as a percentage of total election spending.
A mutation in Tac1p, a transcription factor regulating CDR1 and CDR2, is coupled with loss of heterozygosity at chromosome 5 to mediate antifungal resistance in Candida albicans
Date: 2006-04-01
Creator: Alix Coste
Vincent Turner
Françoise Ischer
Joachim Morschhäuser
Anja, Forche
Anna Selmecki
Judith Berman
Jacques Bille
Dominique Sanglard
Access: Open access
- TAC1, a Candida albicans transcription factor situated near the mating-type locus on chromosome 5, is necessary for the upregulation of the ABC-transporter genes CDR1 and CDR2, which mediate azole resistance. We showed previously the existence of both wild-type and hyperactive TAC1 alleles. Wild-type alleles mediate upregulation of CDR1 and CDR2 upon exposure to inducers such as fluphenazine, while hyperactive alleles result in constitutive high expression of CDR1 and CDR2. Here we recovered TAC1 alleles from two pairs of matched azole-susceptible (DSY294; FH1: heterozygous at mating-type locus) and azole-resistant isolates (DSY296; FH3: homozygous at mating-type locus). Two different TAC1 wild-type alleles were recovered from DSY294 (TAC1-3 and TAC1-4) while a single hyperactive allele (TAC1-5) was isolated from DSY296. A single amino acid (aa) difference between TAC1-4 and TAC1-5 (Asn977 to Asp or N977D) was observed in a region corresponding to the predicted activation domain of Tac1p. Two TAC1 alleles were recovered from FH1 (TAC1-6 and TAC1-7) and a single hyperactive allele (TAC1-7) was recovered from FH3. The N977D change was seen in TAC1-7 in addition to several other aa differences. The importance of N977D in conferring hyperactivity to TAC1 was confirmed by site-directed mutagenesis. Both hyperactive alleles TAC1-5 and TAC1-7 were codominant with wild-type alleles and conferred hyperactive phenotypes only when homozygous. The mechanisms by which hyperactive alleles become homozygous was addressed by comparative genome hybridization and single nucleotide polymorphism arrays and indicated that loss of TAC1 heterozygosity can occur by recombination between portions of chromosome 5 or by chromosome 5 duplication. Copyright © 2006 by the Genetics Society of America.
Resonance in the menstrual cycle: A new model of the LH surge
Date: 2003-01-01
Creator: Mary Lou Zeeman
W. Weckesser
D. Gokhman
Access: Open access
- In vertebrates, ovulation is triggered by a surge of LH from the pituitary. The precise mechanism by which rising oestradiol concentrations initiate the LH surge in the human menstrual cycle remains a fundamental open question of reproductive biology. It is well known that sampling of serum LH on a time scale of minutes reveals pulsatile release from the pituitary in response to pulses of gonadotrophin releasing hormone from the hypothalamus. The LH pulse frequency and amplitude vary considerably over the cycle, with the highest frequency and amplitude at the midcycle surge. Here a new mathematical model is presented of the pituitary as a damped oscillator (pulse generator) driven by the hypothalamus. The model LH surge is consistent with LH data on the time scales of both minutes and days. The model is used to explain the surprising pulse frequency characteristics required to treat human infertility disorders such as Kallmann's syndrome, and new experimental predictions are made.
Extinction in nonautonomous competitive Lotka-Volterra Systems
Date: 1996-01-01
Creator: Francisco Montes De Oca
Mary Lou Zeeman
Access: Open access
- It is well known that for the two species autonomous competitive Lotka-Volterra model with no fixed point in the open positive quadrant, one of the species is driven to extinction, whilst the other population stabilises at its own carrying capacity. In this paper we prove a generalisation of this result to nonautonomous systems of arbitrary finite dimension. That is, for the n species nonautonomous competitive Lotka-Volterra model, we exhibit simple algebraic criteria on the parameters which guarantee that all but one of the species is driven to extinction. The restriction of the system to the remaining axis is a nonautonomous logistic equation, which has a unique solution u(t) that is strictly positive and bounded for all time; see Coleman (Math. Biosci. 45 (1979), 159-173) and Ahmad (Proc. Amer. Math. Soc. 117 (1993), 199-205). We prove in addition that all solutions of the n-dimensional system with strictly positive initial conditions are asymptotic to u(t). © 1996 American Mathematical Society.
Construction and validation of UV-C decontamination cabinets for filtering facepiece respirators: Comment
Date: 2021-07-20
Creator: Anant Agrawal
Joyce Bor
Dale Syphers
Access: Open access
- In their September 2020 paper [Appl. Opt.59, 7585 (2020)], Purschke et al . report UV-C transmittance measurements of N95 filtering facepiece respirators (FFRs), including the 3M 1860, which is one of the most widely used FFRs.We have also measured the transmittance of this FFRin our two separate laboratories with multiple FFR samples, and we have obtained transmittance values similar to one another, but very different from what Purschke et al . reported for two of the four FFR layers.
A 350-year atmospheric history for carbonyl sulfide inferred from Antarctic firn air and air trapped in ice
Date: 2004-11-27
Creator: Stephen A. Montzka
M. Aydin
M. Battle
J. H. Butler
E. S., Saltzman
B. D. Hall
A. D. Clarke
D. Mondeel
J. W. Elkins
Access: Open access
- Carbonyl sulfide (COS) and other trace gases were measured in firn air collected near South Pole (89.98°S) and from air trapped in ice at Siple Dome, Antarctica (81.65°S). The results, when considered with ambient air data and previous ice core measurements, provide further evidence that atmospheric mixing ratios of COS over Antarctica between 1650 and 1850 A.D. were substantially lower than those observed today. Specifically, the results suggest annual mean COS mixing ratios between 300 and 400 pmol mol-1 (ppt) during 1650-1850 A.D. and increases throughout most of the twentieth century. Measurements of COS in modern air and in the upper layers of the firn at South Pole indicate ambient, annual mean mixing ratios between 480 and 490 ppt with substantial seasonal variations. Peak mixing ratios are observed during austral summer in ambient air at South Pole and Cape Grim, Tasmania (40.41°S). Provided COS is not produced or destroyed in firn, these results also suggest that atmospheric COS mixing ratios have decreased 60-90 ppt (10-16%) since the 1980s in high latitudes of the Southern Hemisphere. The history derived for atmospheric mixing ratios of COS in the Southern Hemisphere since 1850 is closely related to historical anthropogenic sulfur emissions. The fraction of anthropogenic sulfur emissions released as COS (directly or indirectly) needed to explain the secular changes in atmospheric COS over this period is 0.3-0.6%. Copyright 2004 by the American Geophysical Union.