1,533 research outputs found
Effects of chilling on the expression of ethylene biosynthetic genes in Passe-Crassane pear (Pyrus communis L.) fruits
Passe-Crassane pears require a 3-month chilling treatment at 0 C to be able to produce ethylene and ripen
autonomously after subsequent rewarming. The chilling treatment strongly stimulated ACC oxidase activity, and
to a lesser extent ACC synthase activity. At the same time, the levels of mRNAs hybridizing to ACC synthase and
ACC oxidase probes increased dramatically. Fruit stored at 18 C immediately after harvest did not exhibit any
of these changes, while fruit that had been previously chilled exhibited a burst of ethylene production associated
with high activity of ACC oxidase and ACC synthase upon rewarming. ACC oxidase mRNA strongly accumulated
in rewarmed fruits, while ACC synthase mRNA level decreased. The chilling-induced accumulation of ACC
synthase and ACC oxidase transcripts was strongly reduced when ethylene action was blocked during chilling with
1-methylcyclopropene (1-MCP). Upon rewarming ACC synthase and ACC oxidase transcripts rapidly disappeared
in 1-MCP-treated fruits. A five-week treatment of non-chilled fruits with the ethylene analog propylene led to
increased expression of ACC oxidase and to ripening. However, ethylene synthesis, ACC synthase activity and
ACC synthasemRNAs remained at very lowlevel. Our data indicate thatACC synthase gene expression is regulated
by ethylene only during, or after chilling treatment, while ACC oxidase gene expression can be induced separately
by either chilling or ethylene
Mechanism of Cyclopropanation Reactions Mediated by (5,10,15,20-Tetra-p-tolylporphyrinato)osmium(II) Complexes
Catalytic systems derived from [Os(TTP)]2 or Fe(TTP) (TTP = 5,10,15,20-tetra-p-tolylporphyrinato) are extremely efficient at converting styrenes and diazo reagents to cyclopropanes in high yields and high stereoselectivity. A number of mechanistic studies have been undertaken to elucidate the catalytic pathway. A mono(carbene) complex, (TTP)OsCHCO2Et, has been isolated but is not the catalytically active species. An electron-withdrawing ligand trans to the carbene in (TTP)OsCHCO2Et activates the carbon fragment toward transfer to an olefin. Labeling studies with (TTP)OsCHX and N2CHY and substrate reactivity profiles are consistent with a trans-osmium(II) bis(carbene) species as the active catalyst
Ethical perspectives on advances in biogerontology
Worldwide populations are aging with economic development as a result of public health initiatives and advances in therapeutic discoveries. Since 1850, life expectancy has advanced by 1 year for every four. Accompanying this change is the rapid development of anti‐aging science. There are three schools of thought in the field of aging science. One perspective is the life course approach, which considers that aging is a good and natural process to be embraced as a necessary and positive aspect of life, where the aim is to improve the quality of existing lifespan and “compress” morbidity. Another view is that aging is undesirable, and that rejuvenation and indeed immortality are possible since the biological basis of aging is understood, and therefore, strategies are possible for engineering negligible senescence. Finally, a hybrid approach is that life span can be extended by anti‐aging medicines but with uncertain effects on health. While these advances offer much promise, the ethical perspectives are seldom discussed in cross‐disciplinary settings. This article discusses some of the key ethical issues arising from recent advances in biogerontology
Shape and Stereoselective Cyclopropanation of Alkenes Catalyzed by Iron Porphyrins
Iron porphryin complexes are active catalysts for the cyclopropanation of alkenes by ethyl diazoacetate. Fe(TIP) (TIP = meso-tetra-p-tolylporphyrin), an isolated iron(II) porphyrin complex, can be used as the catalyst, or the iron(III) complexes of several porphyrins can be reduced in situ. The reactions produce synthetically useful excesses of the trans cyclopropyl ester products. This stereoselectivity exhibits a modest solvent dependence, with donor solvents giving higher ratios of the trans cyclopropane products. The diastereoselectivity exhibits only a modest dependence on the steric bulk of the porphyrin. The reactions are selective for 1-alkenes and 1, 1-disubstituted alkenes. Conjugated substrates and enol ethers react more rapidly than simple aliphatic alkenes. A mechanistic model for the iron-mediated reactions is proposed which is consistent with the data presented herein
On the Asymptotic Validity of the Decoupling Assumption for Analyzing 802.11 MAC Protocol
Performance evaluation of the 802.11 MAC protocol is classically based on the
decoupling assumption, which hypothesizes that the backoff processes at
different nodes are independent. This decoupling assumption results from mean
field convergence and is generally true in transient regime in the asymptotic
sense (when the number of wireless nodes tends to infinity), but, contrary to
widespread belief, may not necessarily hold in stationary regime. The issue is
often related with the existence and uniqueness of a solution to a fixed point
equation; however, it was also recently shown that this condition is not
sufficient; in contrast, a sufficient condition is a global stability property
of the associated ordinary differential equation. In this paper, we give a
simple condition that establishes the asymptotic validity of the decoupling
assumption for the homogeneous case. We also discuss the heterogeneous and the
differentiated service cases and formulate a new ordinary differential
equation. We show that the uniqueness of a solution to the associated fixed
point equation is not sufficient; we exhibit one case where the fixed point
equation has a unique solution but the decoupling assumption is not valid in
the asymptotic sense in stationary regime.Comment: 16 pages, 4 figures, accepted for publication in IEEE Transactions on
Information Theor
Deep Chandra Monitoring Observations of NGC 4649: II. Wide-Field Hubble Space Telescope Imaging of the Globular Clusters
We present g and z photometry and size estimates for globular clusters (GCs)
in the massive Virgo elliptical NGC 4649 (M60) using a five-pointing Hubble
Space Telescope/Advanced Camera for Surveys mosaic. The metal-poor GCs show a
monotonic negative metallicity gradient of (-0.43 +/- 0.10) dex per dex in
radius over the full radial range of the data, out to ~ 24 kpc. There is
evidence for substantial color substructure among the metal-rich GCs. The
metal-poor GCs have typical sizes ~ 0.4 pc larger than the metal-rich GCs out
to large galactocentric distances (~> 20 kpc), favoring an intrinsic
explanation for the size difference rather than projection effects. There is no
clear relation between half-light radius and galactocentric distance beyond ~
15 kpc, suggesting that the sizes of GCs are not generically set by tidal
limitation. Finally, we identify ~ 20 candidate ultra-compact dwarfs that
extend down to surprisingly faint absolute magnitudes (M_z ~ -8.5), and may
bridge the gap between this class and "extended clusters" in the Local Group.
Three of the brighter candidates have published radial velocities and can be
confirmed as bona fide ultra-compact dwarfs; follow-up spectroscopy will
determine the nature of the remainder of the candidates.Comment: ApJ in press. For redacted long table 1, see:
http://www.pa.msu.edu/~strader/4649/table.te
A Chinese Chan-based lifestyle intervention improves memory of older adults
This study aims to explore the potential benefits of a Chinese Chan-based lifestyle intervention on enhancing memory in older people with lower memory function. Forty-four aged 60–83 adults with various level of memory ability participated in the study. Their memories (including verbal and visual components) were assessed before and after 3 months intervention. The intervention consisted of 12 sessions, with one 90 min session per week. The intervention involved components of adopting a special vegetarian diet, practicing a type of mind–body exercises, and learning self-realization. Elderly with lower memory function at the baseline (i.e., their performance on standardized memory tests was within 25th percentile) showed a significant memory improvement after the intervention. Their verbal and visual memory performance has showed 50 and 49% enhancement, respectively. In addition, their improvement can be considered as a reliable and clinically significant change as reflected by their significant pre–post differences and reliable change indices. Such robust treatment effect was found to be specific to memory functions, but less influencing on the other cognitive functions. These preliminary encouraging results have shed some light on the potential applicability of the Chinese Chan-based lifestyle intervention as a method for enhancing memory in the elderly population
Relative Contributions of Geographic, Socioeconomic, and Lifestyle Factors to Quality of Life, Frailty, and Mortality in Elderly
Background: To date, few studies address disparities in older populations specifically using frailty as one of the health outcomes and examining the relative contributions of individual and environmental factors to health outcomes. Methodology/Principal Findings: Using a data set from a health survey of 4,000 people aged 65 years and over living in all regions of Hong Kong, we examined regional variations in self-rated health, frailty, and four-year mortality, and analyzed the relative contributions of lifestyle, socioeconomic status, and geographical location of residence to these outcomes using path analysis. We hypothesize that lifestyle, socioeconomic status, and regional characteristics directly and indirectly through interactions contribute to self-rated physical and psychological health, frailty, and four-year mortality. District variations directly affect self-rated physical health, and also exert an effect through socioeconomic position as well as lifestyle factors. Socioeconomic position in turn directly affects self-rated physical health, as well as indirectly through lifestyle factors. A similar pattern of interaction is observed for self-rated mental health, frailty, and mortality, although there are differences in different lifestyle factors and district associations. Lifestyle factors also directly affect physical and mental components of health, frailty, and mortality. The magnitude of direct district effect is comparable to those of lifestyle and socioeconomic position. Conclusions/Significance: We conclude that district variations in health outcomes exist in the Hong Kong elderl
CEG 453/653: Embedded Systems
ObjectivesTo examine how Chinese people in Hong Kong view healthcareprioritization and to compare the findings with those from a United Kingdom survey.MethodsA cross-sectional opinion survey was conducted in Hong Kong and 1512 participants were interviewed.ResultsData show that the highest rankings were accorded to “treatment for children” and “high technology services.” Services for the elderly, whether in the community or in hospitals, and including end-of-life care, were ranked among the lowest. This view was also shared by healthcare professionals. Compared with the UK findings, there are stark contrasts in the low ranking of end-of-life care and the high ranking of high technology services among the HK population.ConclusionsIt is evident that most people would give priority to the young over the old in distributing a given amount of healthcare services. To meet the needs of ageing societies and to meet the needs of all users equitably, healthcare policy needs to acknowledge constraints and the needs for prioritization. Both the public and professionals should engage with policy makers in formulating a policy based on cost benefit considerations as well as overall societal view of prioritization that is not based on age alone
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