121 research outputs found
Permanent and transitory policy shocks in an empirical macro model with asymmetric information
Despite a large literature documenting that the efficacy of monetary policy depends on how inflation expectations are anchored, many monetary policy models assume: (1) the inflation target of monetary policy is constant; and, (2) the inflation target is known by all economic agents. This paper proposes an empirical specification with two policy shocks: permanent changes to the inflation target and transitory perturbations of the short-term real rate. The public sector cannot correctly distinguish between these two shocks and, under incomplete learning, private perceptions of the inflation target will not equal the true target. The paper shows how imperfect policy credibility can affect economic responses to structural shocks, including transition to a new inflation target - a question that cannot be addressed by many commonly used empirical and theoretical models. In contrast to models where all monetary policy actions are transient, the proposed specification implies that sizable movements in historical bond yields and inflation are attributable to perceptions of permanent shocks in target inflation
Supernovae in Early-Type Galaxies: Directly Connecting Age and Metallicity with Type Ia Luminosity
We have obtained optical spectra of 29 early-type (E/S0) galaxies that hosted
type Ia supernovae (SNe Ia). We have measured absorption-line strengths and
compared them to a grid of models to extract the relations between the
supernova properties and the luminosity-weighted age/composition of the host
galaxies. The same analysis was applied to a large number of early-type field
galaxies selected from the SDSS spectroscopic survey. We find no difference in
the age and abundance distributions between the field galaxies and the SN Ia
host galaxies. We do find a strong correlation suggesting that SNe Ia in
galaxies whose populations have a characteristic age greater than 5 Gyr are ~ 1
mag fainter at V(max) than those found in galaxies with younger populations.
However, the data cannot discriminate between a smooth relation connecting age
and supernova luminosity or two populations of SN Ia progenitors. We find that
SN Ia distance residuals in the Hubble diagram are correlated with host-galaxy
metal abundance, consistent with the predictions of Timmes, Brown & Truran
(2003). The data show that high iron abundance galaxies host less-luminous
supernovae. We thus conclude that the time since progenitor formation primarily
determines the radioactive Ni production while progenitor metal abundance has a
weaker influence on peak luminosity, but one not fully corrected by light-curve
shape and color fitters. Assuming no selection effects in discovering SNe Ia in
local early-type galaxies, we find a higher specific SN Ia rate in E/S0
galaxies with ages below 3 Gyr than in older hosts. The higher rate and
brighter luminosities seen in the youngest E/S0 hosts may be a result of recent
star formation and represents a tail of the "prompt" SN Ia progenitors.Comment: 44 pages, 11 figures, 4 tables; ApJ Accepted (Sept. 20, 2008 issue
Variation in Individual Responses to Time-Restricted Feeding and Resistance Training
Time-restricted feeding (TRF) is a form of intermittent fasting which limits all caloric intake to a certain period of time each day in an attempt to reduce daily energy intake, promote weight loss, and improve health. Resistance training (RT) has been reported to increase muscular strength and improve body composition. Very limited information is available on the combination of TRF and RT. The purpose of this study was to examine the variation in individual body composition, dietary intake, and muscular performance responses to an 8-wk TRF and RT program. Healthy males (n = 20; age = 22 ± 3 y; BMI = 27 ± 6 kg/m2; % fat = 22 ± 6 % wt) were randomized to TRF + RT or RT alone for 8 wks. RT was performed 3 dys/wk and consisted of alternate workouts of upper and lower body using a resistance progression scheme. TRF limited energy intake to a 4-hr period on the 4 dys/wk when RT was not performed. Energy intake was not restricted in either group, and eating times were not specified in the RT alone group. Body composition, muscular performance, and dietary records were assessed at 0, 4, and 8 wks. Inter- and intra-individual variations in outcome measures were estimated by hierarchical linear growth modeling. The amount of variability attributable to characteristics between or within participants was evaluated from variance estimates. For TRF + RT, percent changes ranged from -5.5 to +2.6% for body weight, -22.1 to +9.4% for fat mass, -7.7 to +4.6% for lean body mass, +3.4 to +30.4% for bench press 1-RM, and +10.1 to +67.6% for leg press 1-RM. For RT alone, percent changes ranged from -6.6 to +2.1% for body weight, -14.4 to +12.6% for fat mass, -4.1 to +3.9% for lean body mass, +4.9 to +12.9% for bench press 1-RM, and +14.3 to +37.7% for leg press 1-RM. Percentages of total variability attributed to inter-individual factors ranged from 3.3 to 49.2% for dietary measures, 59.0 to 93.9% for muscular performance, and 97.0 to 99.6% for body composition. Remaining variability was attributed to intra-individual factors. Individual responses to the study interventions varied widely. Differences between individuals were an important source of variability, indicating participant samples should be homogenous and/or quite large to examine changes in body composition or muscular performance using nutrition and exercise interventions
Lack of phenotypic and evolutionary cross-resistance against parasitoids and pathogens in Drosophila melanogaster
BackgroundWhen organisms are attacked by multiple natural enemies, the evolution of a resistance mechanism to one natural enemy will be influenced by the degree of cross-resistance to another natural enemy. Cross-resistance can be positive, when a resistance mechanism against one natural enemy also offers resistance to another; or negative, in the form of a trade-off, when an increase in resistance against one natural enemy results in a decrease in resistance against another. Using Drosophila melanogaster, an important model system for the evolution of invertebrate immunity, we test for the existence of cross-resistance against parasites and pathogens, at both a phenotypic and evolutionary level.MethodsWe used a field strain of D. melanogaster to test whether surviving parasitism by the parasitoid Asobara tabida has an effect on the resistance against Beauveria bassiana, an entomopathogenic fungus; and whether infection with the microsporidian Tubulinosema kingi has an effect on the resistance against A. tabida. We used lines selected for increased resistance to A. tabida to test whether increased parasitoid resistance has an effect on resistance against B. bassiana and T. kingi. We used lines selected for increased tolerance against B. bassiana to test whether increased fungal resistance has an effect on resistance against A. tabida.Results/ConclusionsWe found no positive cross-resistance or trade-offs in the resistance to parasites and pathogens. This is an important finding, given the use of D. melanogaster as a model system for the evolution of invertebrate immunity. The lack of any cross-resistance to parasites and pathogens, at both the phenotypic and the evolutionary level, suggests that evolution of resistance against one class of natural enemies is largely independent of evolution of resistance against the other
Pyruvate kinase M2 activation may protect against the progression of diabetic glomerular pathology and mitochondrial dysfunction
Diabetic nephropathy (DN) is a major cause of end-stage renal disease, and therapeutic options for preventing its progression are limited. To identify novel therapeutic strategies, we studied protective factors for DN using proteomics on glomeruli from individuals with extreme duration of diabetes (≥ 50 years) without DN and those with histologic signs of DN. Enzymes in the glycolytic, sorbitol, methylglyoxal and mitochondrial pathways were elevated in individuals without DN. In particular, pyruvate kinase M2 (PKM2) expression and activity were upregulated. Mechanistically, we showed that hyperglycemia and diabetes decreased PKM2 tetramer formation and activity by sulfenylation in mouse glomeruli and cultured podocytes. Pkm-knockdown immortalized mouse podocytes had higher levels of toxic glucose metabolites, mitochondrial dysfunction and apoptosis. Podocyte-specific Pkm2-knockout (KO) mice with diabetes developed worse albuminuria and glomerular pathology. Conversely, we found that pharmacological activation of PKM2 by a small-molecule PKM2 activator, TEPP-46, reversed hyperglycemia-induced elevation in toxic glucose metabolites and mitochondrial dysfunction, partially by increasing glycolytic flux and PGC-1α mRNA in cultured podocytes. In intervention studies using DBA2/J and Nos3 (eNos) KO mouse models of diabetes, TEPP-46 treatment reversed metabolic abnormalities, mitochondrial dysfunction and kidney pathology. Thus, PKM2 activation may protect against DN by increasing glucose metabolic flux, inhibiting the production of toxic glucose metabolites and inducing mitochondrial biogenesis to restore mitochondrial function
The UV-Optical Color Dependence of Galaxy Clustering in the Local Universe
We measure the UV-optical color dependence of galaxy clustering in the local
universe. Using the clean separation of the red and blue sequences made
possible by the NUV - r color-magnitude diagram, we segregate the galaxies into
red, blue and intermediate "green" classes. We explore the clustering as a
function of this segregation by removing the dependence on luminosity and by
excluding edge-on galaxies as a means of a non-model dependent veto of highly
extincted galaxies. We find that \xi (r_p, \pi) for both red and green galaxies
shows strong redshift space distortion on small scales -- the "finger-of-God"
effect, with green galaxies having a lower amplitude than is seen for the red
sequence, and the blue sequence showing almost no distortion. On large scales,
\xi (r_p, \pi) for all three samples show the effect of large-scale streaming
from coherent infall. On scales 1 Mpc/h < r_p < 10 Mpc/h, the projected
auto-correlation function w_p(r_p) for red and green galaxies fits a power-law
with slope \gamma ~ 1.93 and amplitude r_0 ~ 7.5 and 5.3, compared with \gamma
~ 1.75 and r_0 ~ 3.9 Mpc/h for blue sequence galaxies. Compared to the
clustering of a fiducial L* galaxy, the red, green, and blue have a relative
bias of 1.5, 1.1, and 0.9 respectively. The w_p(r_p) for blue galaxies display
an increase in convexity at ~ 1 Mpc/h, with an excess of large scale
clustering. Our results suggest that the majority of blue galaxies are likely
central galaxies in less massive halos, while red and green galaxies have
larger satellite fractions, and preferentially reside in virialized structures.
If blue sequence galaxies migrate to the red sequence via processes like
mergers or quenching that take them through the green valley, such a
transformation may be accompanied by a change in environment in addition to any
change in luminosity and color.Comment: accepted by MNRA
Modelling element abundances in semi-analytic models of galaxy formation
We update the treatment of chemical evolution in the Munich semi-analytic model, L-GALAXIES. Our new implementation includes delayed enrichment from stellar winds, supernovae type II (SNe-II) and supernovae type Ia (SNe-Ia), as well as metallicity-dependent yields and a reformulation of the associated supernova feedback. Two different sets of SN-II yields and three different SN-Ia delay-time distributions (DTDs) are considered, and eleven heavy elements (including O, Mg and Fe) are self-consistently tracked. We compare the results of this new implementation with data on a) local, star-forming galaxies, b) Milky Way disc G dwarfs, and c) local, elliptical galaxies. We find that the z=0 gas-phase mass-metallicity relation is very well reproduced for all forms of DTD considered, as is the [Fe/H] distribution in the Milky Way disc. The [O/Fe] distribution in the Milky Way disc is best reproduced when using a DTD with less than or equal to 50 per cent of SNe-Ia exploding within ~400 Myrs. Positive slopes in the mass-[alpha/Fe] relations of local ellipticals are also obtained when using a DTD with such a minor `prompt' component. Alternatively, metal-rich winds that drive light alpha elements directly out into the circumgalactic medium also produce positive slopes for all forms of DTD and SN-II yields considered. Overall, we find that the best model for matching the wide range of observational data considered here should include a power-law SN-Ia DTD, SN-II yields that take account of prior mass loss through stellar winds, and some direct ejection of light alpha elements out of galaxies
The Formation of Dust Lanes: Implications for Galaxy Evolution
We find that disk galaxies show a sharp, mass-dependent transition in the
structure of their dusty ISM. Dust lanes are a generic feature of massive disks
with V_rot>120km/s, but are completely absent in galaxies with V_rot<120km/s.
The transition reflects an increase in the scale height of the cold ISM in low
mass galaxies, driven by larger turbulent velocities supporting the gas layer,
rather than sharp drops in the gas surface density. We identify the
V_rot=120km/s transition with the onset of gravitational instabilities in high
mass galaxies. The instabilities lead to fragmentation and gravitational
collapse along spiral arms, smaller gas scale heights, lower turbulent
velocities, and thus to narrow dust lanes. The drop in velocity dispersion may
be due either to a switch in the driving mechanism for turbulence or to a
change in the response of the ISM to supernovae after the ISM has collapsed to
a dense layer. The resulting smaller gas scale height can lead to significant
increases in the star formation rate when disk instabilities are present, and
may explain the Kennicutt surface density threshold for star formation. Our
data suggest that star formation will be systematically less efficient in low
mass disks with V_c<120km/s, leading to star formation timescales longer than
the gas accretion timescale. This effect can suppress the metallicity and
nucleosynthetic yields of low mass disks, and thus explain the disk
mass-metallicity relationship without invoking galactic SN-driven outflows. The
transitions in disk stability, dust structure, and/or star formation efficiency
may also be responsible for observed changes in the slope of the Tully-Fisher
relation, in the sharp increase in the thickness of dwarf galaxy disks, and in
the onset of bulges in galaxies with V_rot>120km/s. (Abridged)Comment: 20 pages, Accepted by the Astrophysical Journa
Muscle inactivation of mTOR causes metabolic and dystrophin defects leading to severe myopathy
mTor, acting mainly via mTORC1, controls dystrophin transcription in a raptor- and rictor-independent mechanism
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