1,721,261 research outputs found
A polynomial upper bound for the mixing time of edge rotations on planar maps
Full text linkWe consider a natural local dynamic on the set of all rooted planar maps with n edges that is in some sense analogous to “edge flip” Markov chains, which have been considered before on a variety of combinatorial structures (triangulations of the n-gon and quadrangulations of the sphere, among others). We provide the first polynomial upper bound for the mixing time of this “edge rotation” chain on planar maps: we show that the spectral gap of the edge rotation chain is bounded below by an appropriate constant times n−11/2. In doing so, we provide a partially new proof of the fact that the same bound applies to the spectral gap of edge flips on quadrangulations as defined in [8], which makes it possible to generalise the result of [8] to a variant of the edge flip chain related to edge rotations via Tutte’s bijection
The scaling limit of random outerplanar maps
Full text link A planar map is outerplanar if all its vertices belong to the same face. We show that random uniform outerplanar maps with n vertices suitably rescaled by a factor 1/n−−√ converge in the Gromov–Hausdorff sense to 72–√/9 times Aldous’ Brownian tree. The proof uses the bijection of Bonichon, Gavoille and Hanusse (J. Graph Algorithms Appl. 9 (2005) 185–204). </p
Polynomial mixing time of edge flips on quadrangulations
Full text linkWe establish the first polynomial upper bound for the mixing time of random edge flips on rooted quadrangulations: we show that the spectral gap of the edge flip Markov chain on quadrangulations with n faces admits, up to constants, an upper bound of n- 5 / 4 and a lower bound of n- 11 / 2. In order to obtain the lower bound, we also consider a very natural Markov chain on plane trees—or, equivalently, on Dyck paths—and improve the previous lower bound for its spectral gap by Shor and Movassagh
Delirium: Acute Confusional States in Palliative Medicine
No full textDelirium is among the most prevalent and challenging clinical problems. Its assessment and management must be individualized based on both a biomedical understanding of the disease and its comorbidities, and a more nuanced understanding of prognosis, risks and benefits of treatment. Every intervention must be informed by a critical understanding of the changing goals of care. These complexities are critically explored in this volume. Given the diversity of clinical presentations associated with neurological and psychiatric disorders in the medically ill, considerable efforts have been made during the past decade to derive meaningful diagnostic criteria for delirium. Consensus on diagnostic criteria are needed as a foundation for future investigations focused on the epidemiology, etiologies, and treatments of this disorder. Even distinctions that appear simple in some populations, such as the difference between delirium and dementia, can become clouded when an underlying disease is progressing and the patient is exposed to complex therapies for the disease itself and for its consequences. If an acute confusional state that is expected to be transitory never clears, should it still be called a delirium? If one or two of the elements that together characterize delirium—for example, changes in alertness, psychomotor activity, cognition, perception, mood, or sleep-wake cycle—occur in isolation, is this delirium?
The development of validated measures to identify delirium, and grade its severity, have been an important advance. They highlight the need for additional studies that will clarify the phenomenology of delirium, establish evidence-based criteria for diagnosis, and rationalize the type of clinical assessment that is needed to define a treatment strategy. Studies that separately assess consciousness, cognition, perception, and mood potentially could define subpopulations that may benefit from more targeted interventions. Ultimately, treatable pathophysiologies linked to a particular phenomenology might be elucidated.
Even the most sophisticated research, however, will never obviate the clinical challenge in managing delirium in populations with advanced illness. Death is commonly preceded by a period of somnolence or confusion, which may be as brief as hours or as long as months. Although the decline might be attributable to specific biomedical causes, it is not considered pathologic if it is perceived to be part of the normal dying process. If this is the case, interventions are limited to those necessary to ensure comfort and reassure the family. Efforts to assess and reverse the underlying causes, which are essential in other clinical settings, would be inappropriate then.
Thus, the clinical problem of delirium resonates with a broad range of profound challenges in palliative care. Clinicians are notoriously poor prognosticators, yet some understanding of the time left is needed to inform judgments about the evaluation and management of delirium. If there is a chance for meaningful survival, and the goals of care are consistent with this, the delirious patient may undergo a very aggressive evaluation and complex interventions designed to reduce contributing causes and reverse the disorder. If the patient is perceived to be imminently dying, however, the overriding concern may be the control of agitation or fear. No effort is made to identify or treat potential causes.
Ethical considerations are prominent in this decision making and are under intense discussion among specialists in palliative care. Should the delirious patient at the end of life empirically receive hydration, a simple intervention that would reverse one potential contributing factor? Or does the belief that death is imminent preclude this intervention? If the delirious patient is agitated, what are the ethical considerations in using sedative doses of drugs until death occurs? These are complex issues, and require case-by-case reasoning.
The management of delirium requires excellent communication, a fundamental aspect of the broader effort to provide palliative care. If an understanding of the patient’s and family’s expectations and values is obtained before the patient loses capacity for decision making, the subsequent course may be less conflicted. If the patient has a surrogate for decision making, communication with this person, and the rest of the family, is key once the patient is unable to express desires.
The scientific and clinical characterization of delirium is yet rudimentary, but clinicians must do the best they can. The critical evaluation of the existing literature that is combined in this volume with the Authors’ personal experience and a number of practical examples can provide a good foundation for the challenges faced at the bedside
Delirium: Acute Confusional States in Palliative Medicine. Second Edition
No full textDelirium is a complex syndrome with a multifactorial aetiology and is characterized by marked disturbances of consciousness, attention, memory, perception, thought, sleep-wake cycle, and by fluctuation of symptoms. This book covers in detail the pathophysiology, epidemiology, clinical aspects, differential diagnosis, and management of the syndrome.
Due to the special characteristics of the syndrome, specific chapters deal with different aetiologies and populations at risk, with emphasis on the critically ill and palliative care patients. As delirium often announces or anticipates the proximity of death, family issues are considered in a comprehensive final chapter, covering the impact of terminal illness on the family and the process of bereavement. The book emphasises the need for assessing and diagnosing delirium with reliable instruments, and a chapter on assessment is reinforced by including appendices of many of the most relevant instruments reported in recent literature. The evidence from the literature is always distinguished from the authors' opinions and most chapters are integrated by the presentation of case examples. Updated for the second edition this book contains new material on topics including classification systems, more data on populations at risk, and significant new material on the family and bereavement. Delirium: Acute confusional states in palliative medicine, Second Edition demonstrates that only an interdisciplinary treatment of delirium between neurology, psychiatry and palliative medicine can develop knowledge of the syndrome and improve patient and family care.
This book has been written for palliative care physicians and specialist nurses, neurologists, psychiatrists, and other health professionals treating terminally ill patients, offering them a clear account of how to recognize and deal with the syndrome.
Features of the book: Delirium is the most common neuro-psychiatric complication encountered by patients in the terminal phase of illness; Palliative care physicians and nurses are among the most frequent observers of delirium in medicine; Provides palliative care physicians with a clear account of how to recognise and treat delirium; Takes a multi-disciplinary approach crossing the fields of palliative medicine, neurology, psychiatry, and oncology; Encourages a more integrated approach when dealing with terminally ill patients and their families; Contains new material on topics such as classification systems, more data on populations at risk, and significant new material on the family and bereavement
A Theorethical Comparison of Various VVA Systems for Performance and Emission Improvements of SI-Engines
No full textalso in "Variable Valve Actuation 2001", SAE SP-1599, ISBN 0-7680-0746-
Palliative sedation: Ethical aspects
No full textPalliative sedation (PS), the medical act of decreasing a patient's awareness to relieve otherwise intractable suffering, is considered by some commentators to be controversial because of its consequences on residual survival and/or quality of life, and to be inappropriate for treating pure existential suffering. We will argue that PS must be always proportional, i.e. controlling refractory symptoms while keeping the loss of personal values (communication, affective relationships, care relationship) as low as possible, and that imminence of death is necessary too, from an ethical point of view, if a deep and continuous sedation (DCS) is proposed. Moreover, in case of pure existential suffering DCS should only be considered after repeated trials of respite sedation. The use of progressive consent and advance care planning to share the decision with the patient and to involve the family in the decision process as much as the patient desires is another ethical aspect to be pursued. Producing, implementing and sustaining guidelines at the higher scientific and professional level promise to help in improving both clinical and ethical aspects of the practice of PS
Bijections for ranked tree-child networks
Full text linkThe class of ranked tree-child networks, tree-child networks arising from an evolution process with a fixed embedding into the plane, has recently been introduced by Bienvenu, Lambert, and Steel. These authors derived counting results for this class. In this note, we will give bijective proofs of three of their results. Two of our bijections answer questions raised in their paper
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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