103 research outputs found
Unknown I.I.D. Prophets: Better Bounds, Streaming Algorithms, and a New Impossibility
A prophet inequality states, for some α ∈ [0, 1], that the expected value achievable by a gambler who
sequentially observes random variables X1, . . . , Xn and selects one of them is at least an α fraction
of the maximum value in the sequence. We obtain three distinct improvements for a setting that
was first studied by Correa et al. (EC, 2019) and is particularly relevant to modern applications in
algorithmic pricing. In this setting, the random variables are i.i.d. from an unknown distribution and
the gambler has access to an additional βn samples for some β ≥ 0. We first give improved lower
bounds on α for a wide range of values of β; specifically, α ≥ (1 + β)/e when β ≤ 1/(e − 1), which is
tight, and α ≥ 0.648 when β = 1, which improves on a bound of around 0.635 due to Correa et al.
(SODA, 2020). Adding to their practical appeal, specifically in the context of algorithmic pricing,
we then show that the new bounds can be obtained even in a streaming model of computation
and thus in situations where the use of relevant data is complicated by the sheer amount of data
available. We finally establish that the upper bound of 1/e for the case without samples is robust
to additional information about the distribution, and applies also to sequences of i.i.d. random
variables whose distribution is itself drawn, according to a known distribution, from a finite set of
known candidate distributions. This implies a tight prophet inequality for exchangeable sequences
of random variables, answering a question of Hill and Kertz (Contemporary Mathematics, 1992),
but leaves open the possibility of better guarantees when the number of candidate distributions is
small, a setting we believe is of strong interest to applications
Investigations into the molecular and physiological factors influencing low temperature breakdown in stonefruit
Cold storage is essential for the successful distribution of stonefruit to distant markets; however most cultivars suffer chilling injury (CI), commonly referred to as low temperature breakdown (LTB). LTB is a significant problem for industry and the genetic factors responsible for its onset are not understood. Treatment of stonefruit with the ethylene antagonist, 1-methylcyclopropene (1-MCP) before cold
storage has been shown to differentially affect the development of CI in peaches and plums. 1-MCP treatment increases the incidence of LTB in peaches but reduces it in plums (Fernández-Trujillo and Artés, 1997; Fan et al., 2002). These observations were confirmed and preliminary research into the effects of 1-MCP and cold storage
on gene expression is reported herein
Hubble Space Telescope survey of Magellanic Cloud star clusters. Photometry and astrometry of 113 clusters and early results
In the past years, we have undertaken an extensive investigation of LMC and
SMC star clusters based on HST data. We present photometry and astrometry of
stars in 101 fields observed with the WFC/ACS, UVIS/WFC3 and NIR/WFC3 cameras.
These fields comprise 113 star clusters. We provide differential-reddening maps
and illustrate various scientific outcomes that arise from the early inspection
of the photometric catalogs. In particular, we provide new insights on the
extended main-sequence turn-off (eMSTO) phenomenon: i) We detected eMSTOs in
two clusters, KMHK361 and NGC265, which had no previous evidence of multiple
populations. This finding corroborates the conclusion that the eMSTO is a
widespread phenomenon among clusters younger than ~2 Gyr. ii) The homogeneous
color-magnitude diagrams (CMDs) of 19 LMC clusters reveal that the distribution
of stars along the eMSTO depends on cluster age. iii) We discovered a new
feature along the eMSTO of NGC1783, which consists of a distinct group of stars
going on the red side of the eMSTO in CMDs composed of ultraviolet filters.
Furthermore, we derived the proper motions of stars in the fields of view of
clusters with multi-epoch images. Proper motions allowed us to separate the
bulk of bright field stars from cluster members and investigate the internal
kinematics of stellar populations in various LMC and SMC fields. As an example,
we analyze the field around NGC346 to disentangle the motions of its stellar
populations, including NGC364 and BS90, young and pre-MS stars in the
star-forming region associated with NGC346, and young and old field stellar
populations of the SMC. Based on these results and the fields around five
additional clusters, we find that young SMC stars exhibit elongated
proper-motion distributions that point toward the LMC, thus bringing new
evidence for a kinematic connection between the LMC and SMC.Comment: 37 pages, 27 figures, accepted for publication in Astronomy &
Astrophysic
Bone health and body composition in transgender adults before gender-affirming hormonal therapy: data from the COMET study
Purpose: Preliminary data suggested that bone mineral density (BMD) in transgender adults before initiating gender-affirming hormone therapy (GAHT) is lower when compared to cisgender controls. In this study, we analyzed bone metabolism in a sample of transgender adults before GAHT, and its possible correlation with biochemical profile, body composition and lifestyle habits (i.e., tobacco smoke and physical activity). Methods: Medical data, smoking habits, phospho-calcic and hormonal blood tests and densitometric parameters were collected in a sample of 125 transgender adults, 78 Assigned Females At Birth (AFAB) and 47 Assigned Males At Birth (AMAB) before GAHT initiation and 146 cisgender controls (57 females and 89 males) matched by sex assigned at birth and age. 55 transgender and 46 cisgender controls also underwent a complete body composition evaluation and assessment of physical activity using the International Physical Activity Questionnaire (IPAQ). Results: 14.3% of transgender and 6.2% of cisgender sample, respectively, had z-score values < -2 (p = 0.04). We observed only lower vitamin D values in transgender sample regarding biochemical/hormonal profile. AFAB transgender people had more total fat mass, while AMAB transgender individuals had reduced total lean mass as compared to cisgender people (53.94 ± 7.74 vs 58.38 ± 6.91, p < 0.05). AFAB transgender adults were more likely to be active smokers and tend to spend more time indoor. Fat Mass Index (FMI) was correlated with lumbar and femur BMD both in transgender individuals, while no correlations were found between lean mass parameters and BMD in AMAB transgender people. Conclusions: Body composition and lifestyle factors could contribute to low BMD in transgender adults before GAHT
Is increased time to diagnosis and treatment in symptomatic cancer associated with poorer outcomes?:Systematic review
background: It is unclear whether more timely cancer diagnosis brings favourable outcomes, with much of the previous evidence, in some cancers, being equivocal. We set out to determine whether there is an association between time to diagnosis, treatment and clinical outcomes, across all cancers for symptomatic presentations. methods: Systematic review of the literature and narrative synthesis. results: We included 177 articles reporting 209 studies. These studies varied in study design, the time intervals assessed and the outcomes reported. Study quality was variable, with a small number of higher-quality studies. Heterogeneity precluded definitive findings. The cancers with more reports of an association between shorter times to diagnosis and more favourable outcomes were breast, colorectal, head and neck, testicular and melanoma. conclusions: This is the first review encompassing many cancer types, and we have demonstrated those cancers in which more evidence of an association between shorter times to diagnosis and more favourable outcomes exists, and where it is lacking. We believe that it is reasonable to assume that efforts to expedite the diagnosis of symptomatic cancer are likely to have benefits for patients in terms of improved survival, earlier-stage diagnosis and improved quality of life, although these benefits vary between cancers
On the role of ethylene, auxin and a GOLVEN-like peptide hormone in the regulation of peach ripening
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