225 research outputs found
Elliptic curves of large rank and small conductor
For r=6,7,...,11 we find an elliptic curve E/Q of rank at least r and the
smallest conductor known, improving on the previous records by factors ranging
from 1.0136 (for r=6) to over 100 (for r=10 and r=11). We describe our search
methods, and tabulate, for each r=5,6,...,11, the five curves of lowest
conductor, and (except for r=11) also the five of lowest absolute discriminant,
that we found.Comment: 16 pages, including tables and one .eps figure; to appear in the
Proceedings of ANTS-6 (June 2004, Burlington, VT). Revised somewhat after
comments by J.Silverman on the previous draft, and again to get the correct
page break
Spin-current modulation and square-wave transmission through periodically stubbed electron waveguides
Ballistic spin transport through waveguides, with symmetric or asymmetric
double stubs attached to them periodically, is studied systematically in the
presence of a weak spin-orbit coupling that makes the electrons precess. By an
appropriate choice of the waveguide length and of the stub parameters injected
spin-polarized electrons can be blocked completely and the transmission shows a
periodic and nearly square-type behavior, with values 1 and 0, with wide gaps
when only one mode is allowed to propagate in the waveguide. A similar behavior
is possible for a certain range of the stub parameters even when two-modes can
propagate in the waveguide and the conductance is doubled. Such a structure is
a good candidate for establishing a realistic spin transistor. A further
modulation of the spin current can be achieved by inserting defects in a
finite-number stub superlattice. Finite-temperature effects on the spin
conductance are also considered.Comment: 19 pages, 8 figure
Patient Acceptability of the Yorkshire Dialysis Decision Aid (YoDDA) Booklet: A Prospective Non-Randomized Comparison Study Across 6 Predialysis Services
Background: Patients are satisfied with their kidney care but want more support in making dialysis choices. Predialysis leaflets vary across services, with few being sufficient to enable patients’ informed decision making. We describe the acceptability of a patient decision aid and feasibility of evaluating its effectiveness within usual predialysis practice. Methods: Prospective non-randomized comparison design, Usual Care or Usual Care Plus Yorkshire Dialysis Decision Aid Booklet (+YoDDA), in 6 referral centers (Yorkshire-Humber, UK) for patients with sustained deterioration of kidney function. Consenting (C) patients completed questionnaires after predialysis consultation (T1), and 6 weeks later (T2). Measures assessed YoDDA’s utility to support patients’ decisions and integration within usual care. Results: Usual Care (n = 105) and +YoDDA (n = 84) participant characteristics were similar: male (62%), white (94%), age (mean = 62.6; standard deviation [SD] 14.4), kidney disease severity (glomerular filtration rate [eGFR] mean = 14.7; SD 3.7); decisional conflict was <25; choice-preference for home versus hospital dialysis approximately 50:50. Patients valued receiving YoDDA, reading it on their own (96%), and sharing it with family (72%). +YoDDA participants had higher scores for understanding kidney disease, reasoning about options, feeling in control, sharing their decision with family. Study engagement varied by center (estimated range 14 – 49%; mean 45%); participants varied in completion of decision quality measures. Conclusions: Receiving YoDDA as part of predialysis education was valued and useful to patients with worsening kidney disease. Integrating YoDDA actively within predialysis programs will meet clinical guidelines and patient need to support dialysis decision making in the context of patients’ lifestyle
Insolation forcing of coccolithophore productivity in the North Atlantic during the Middle Pleistocene
Coccolithophores play a key role in the oceanic carbon cycle through the biological and carbonate pumps. Understanding controls on coccolithophore productivity is thus fundamental to quantify oceanic carbon cycling. We investigate changes in coccolithophore productivity over several Pleistocene glacial-interglacial cycles using a high-resolution coccolith Sr/Ca ratio record, which is an indicator of growth rate and thus a proxy for coccolithophore productivity. We use Middle Pleistocene sediments from the North Atlantic Integrated Ocean Drilling Program (IODP) Site U1313 (41.00′ N, 32.58’ W) spanning Marine Isotopic Stages 16 to 10 (638–356 kyr). The location of the record allows us to investigate processes affecting productivity in a mid-latitude setting and to unravel the effects of temperature and regional ocean circulation. Coccolithophore productivity shows a dominant glacial-interglacial cyclicity with higher productivity during glacials, which appears to reflect the southward migration of the North Atlantic high productivity zone currently located between 45° and 55° N. Spectral analysis of the productivity record reveals a suborbital variability consistent with forcing by insolation maxima superimposed on the front migration pattern. Similar to today, coccolithophore productivity during interglacials was enhanced when insolation was at its maximum in spring or in autumn, whereas during glacials, productivity was enhanced when summer/autumn insolation was at its maximum. We show that in the studied region, coccolithophore productivity was driven by processes reflecting regional insolation. Applying this information to model experiments is required to assess if coccolithophore productivity played a significant role in past changes of atmospheric CO2
Low Complexity Regularization of Linear Inverse Problems
Inverse problems and regularization theory is a central theme in contemporary
signal processing, where the goal is to reconstruct an unknown signal from
partial indirect, and possibly noisy, measurements of it. A now standard method
for recovering the unknown signal is to solve a convex optimization problem
that enforces some prior knowledge about its structure. This has proved
efficient in many problems routinely encountered in imaging sciences,
statistics and machine learning. This chapter delivers a review of recent
advances in the field where the regularization prior promotes solutions
conforming to some notion of simplicity/low-complexity. These priors encompass
as popular examples sparsity and group sparsity (to capture the compressibility
of natural signals and images), total variation and analysis sparsity (to
promote piecewise regularity), and low-rank (as natural extension of sparsity
to matrix-valued data). Our aim is to provide a unified treatment of all these
regularizations under a single umbrella, namely the theory of partial
smoothness. This framework is very general and accommodates all low-complexity
regularizers just mentioned, as well as many others. Partial smoothness turns
out to be the canonical way to encode low-dimensional models that can be linear
spaces or more general smooth manifolds. This review is intended to serve as a
one stop shop toward the understanding of the theoretical properties of the
so-regularized solutions. It covers a large spectrum including: (i) recovery
guarantees and stability to noise, both in terms of -stability and
model (manifold) identification; (ii) sensitivity analysis to perturbations of
the parameters involved (in particular the observations), with applications to
unbiased risk estimation ; (iii) convergence properties of the forward-backward
proximal splitting scheme, that is particularly well suited to solve the
corresponding large-scale regularized optimization problem
Layered control architectures in robots and vertebrates
We revieiv recent research in robotics, neuroscience, evolutionary neurobiology, and ethology with the aim of highlighting some points of agreement and convergence. Specifically, we com pare Brooks' (1986) subsumption architecture for robot control with research in neuroscience demonstrating layered control systems in vertebrate brains, and with research in ethology that emphasizes the decomposition of control into multiple, intertwined behavior systems. From this perspective we then describe interesting parallels between the subsumption architecture and the natural layered behavior system that determines defense reactions in the rat. We then consider the action selection problem for robots and vertebrates and argue that, in addition to subsumption- like conflict resolution mechanisms, the vertebrate nervous system employs specialized selection mechanisms located in a group of central brain structures termed the basal ganglia. We suggest that similar specialized switching mechanisms might be employed in layered robot control archi tectures to provide effective and flexible action selection
EXPLORE: A Prospective, Multinational, Natural History Study of Patients with Acute Hepatic Porphyria with Recurrent Attacks
BACKGROUND AND AIMS: Acute hepatic porphyria
comprises a group of rare genetic diseases caused by mutations in genes involved in heme biosynthesis. Patients can
experience acute neurovisceral attacks, debilitating chronic
symptoms, and long-term complications. There is a lack of
multinational, prospective data characterizing the disease and
current treatment practices in severely affected patients.
APPROACH AND RESULTS: EXPLORE is a prospective,
multinational, natural history study characterizing disease activity and clinical management in patients with acute hepatic
porphyria who experience recurrent attacks. Eligible patients
had a confirmed acute hepatic porphyria diagnosis and had
experienced ≥3 attacks in the prior 12 months or were receiving prophylactic treatment. A total of 112 patients were enrolled and followed for at least 6 months. In the 12 months
before the study, patients reported a median (range) of 6
(0-52) acute attacks, with 52 (46%) patients receiving hemin
prophylaxis. Chronic symptoms were reported by 73 (65%)
patients, with 52 (46%) patients experiencing these daily.
During the study, 98 (88%) patients experienced a total of
483 attacks, 77% of which required treatment at a health
care facility and/or hemin administration (median [range] annualized attack rate 2.0 [0.0-37.0]). Elevated levels of hepatic
δ-aminolevulinic acid synthase 1 messenger ribonucleic acid levels, δ-aminolevulinic acid, and porphobilinogen compared with
the upper limit of normal in healthy individuals were observed
at baseline and increased further during attacks. Patients had
impaired quality of life and increased health care utilization.
CONCLUSIONS: Patients experienced attacks often requiring treatment in a health care facility and/or with hemin, as
well as chronic symptoms that adversely influenced day-to-day
functioning. In this patient group, the high disease burden
and diminished quality of life highlight the need for novel
therapies. (Hepatology 2020;71:1546-1558)
EXPLORE: A prospective, multinational natural history study of patients with acute hepatic porphyria with recurrent attacks
BACKGROUND AND AIMS: Acute hepatic porphyria
comprises a group of rare genetic diseases caused by mutations in genes involved in heme biosynthesis. Patients can
experience acute neurovisceral attacks, debilitating chronic
symptoms, and long-term complications. There is a lack of
multinational, prospective data characterizing the disease and
current treatment practices in severely affected patients.
APPROACH AND RESULTS: EXPLORE is a prospective,
multinational, natural history study characterizing disease activity and clinical management in patients with acute hepatic
porphyria who experience recurrent attacks. Eligible patients
had a confirmed acute hepatic porphyria diagnosis and had
experienced ≥3 attacks in the prior 12 months or were receiving prophylactic treatment. A total of 112 patients were enrolled and followed for at least 6 months. In the 12 months
before the study, patients reported a median (range) of 6
(0-52) acute attacks, with 52 (46%) patients receiving hemin
prophylaxis. Chronic symptoms were reported by 73 (65%)
patients, with 52 (46%) patients experiencing these daily.
During the study, 98 (88%) patients experienced a total of
483 attacks, 77% of which required treatment at a health
care facility and/or hemin administration (median [range] annualized attack rate 2.0 [0.0-37.0]). Elevated levels of hepatic
δ-aminolevulinic acid synthase 1 messenger ribonucleic acid levels, δ-aminolevulinic acid, and porphobilinogen compared with
the upper limit of normal in healthy individuals were observed
at baseline and increased further during attacks. Patients had
impaired quality of life and increased health care utilization.
CONCLUSIONS: Patients experienced attacks often requiring treatment in a health care facility and/or with hemin, as
well as chronic symptoms that adversely influenced day-to-day
functioning. In this patient group, the high disease burden
and diminished quality of life highlight the need for novel
therapies. (Hepatology 2020;71:1546-1558)
Self-help groups challenge health care systems in the US and UK
Purpose: This research considers how self-help groups (SHGs) and self- help organizations (SHOs) contribute to consumerist trends in two different societies: United States and United Kingdom. How do the health care systems and the voluntary sectors affect the kinds of social changes that SHGs/SHOs make?
Methodology/approach: A review of research on the role of SHGs/SHOs in contributing to national health social movements in the UK and US was made. Case studies of the UK and the US compare the characteristics of their health care systems and their voluntary sector. Research reviews of two community level self-help groups in each country describe the kinds of social changes they made.
Findings: The research review verified that SHGs/SHOs contribute to national level health social movements for patient consumerism. The case studies showed that community level SHGs/SHOs successfully made the same social changes but on a smaller scale as the national movements, and the health care system affects the kinds of community changes made.
Research limitations: A limited number of SHGs/SHOs within only two societies were studied. Additional SHGs/SHOs within a variety of societies need to be studied.
Originality/value of chapter
Community SHGs/SHOs are often trivialized by social scientists as just inward-oriented support groups, but this chapter shows that local groups contribute to patient consumerism and social changes but in ways that depend on the kind of health care system and societal context
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