Momentum space tomographic imaging of photoelectrons

We apply tomography, a general method for reconstructing 3-D distributions from multiple projections, to reconstruct the momentum distribution of electrons produced via strong field photoionization. The projections are obtained by rotating the electron distribution via the polarization of the ionizing laser beam and recording a momentum spectrum at each angle with a 2-D velocity map imaging spectrometer. For linearly polarized light the tomographic reconstruction agrees with the distribution obtained using an Abel inversion. Electron tomography, which can be applied to any polarization, will simplify the technology of electron imaging. The method can be directly generalized to other charged particles.Comment: Accepted by J. Phys.

Alignment dependent enhancement of the photo-electron cutoff for multi-photon ionization of molecules

The multiphoton ionization rate of molecules depends on the alignment of the molecular axis with respect to the ionizing laser polarization. By studying molecular frame photo-electron angular distributions from N$_2$, O$_2$ and benzene, we illustrate how the angle-dependent ionization rate affects the photo-electron cutoff energy. We find alignment can enhance the high energy cutoff of the photo-electron spectrum when probing along a nodal plane or when ionization is otherwise suppressed. This is supported by calculations using a tunneling model with a single ion state.Comment: 4 pages, 4 figure

Postmortem investigations on winter stranded sperm whales from the coasts of Belgium and the Netherlands

During winter 1994-95, four and three sperm whales (Physeter macrocephalus) were stranded along the Belgian and the Dutch coasts, respectively. Necropsies and tissue samplings were collected 24 hrs post mortem. Lesions on several whales included round and linear skin scars, ventral skin abrasions, acute skin ulcers, acute ulcerative stomatitides, acute to chronic external otitides, and passive visceral congestion. In addition, these sperm whales appeared to be debilitated with severe weight deficit, had blubber thickness reduction, the absence of abdominal fat, and the intestinal tracts were almost empty. Three categories of lesions and their possible relation with the stranding were evaluated. Cutaneous scars observed on the seven whales appeared to have no relation with the stranding. The poor body condition and acute integument ulcerative lesions were present before the stranding. Ventral skin abrasions and visceral passive congestion were caused by the strandings. Absence of food in the alimentary tracts, evidence of weight loss and blubber thickness reduction were compatible with an extended presence of the sperm whales in the North Sea, where adequate food is not available. This might lead to progressive weakness, predisposing the animals to secondary pathogens such as viral diseases. Finally, the coastal configuration of the southern North Sea makes it a trap for sperm whales which have entered the area during their wanderings

Platypnea-orthodeoxia due to osteoporosis and severe kyphosis: a rare cause for dyspnea and hypoxemia

Platypnea orthodeoxia is a rare disorder characterized by dyspnea and arterial desaturation, exacerbated by the upright position and relieved when the subject is recumbent. We report the case of a 79-year old woman admitted to hospital with dyspnea who was thought to have restrictive ventilatory impairment due to osteoporosis and severe kyphosis. Interestingly, the dyspnea was aggravated in the upright position, whereas the symptoms improved in the supine position. Arterial blood gas analysis confirmed orthodeoxia. The lung function test showed only a mild obstructive and restrictive ventilation disorder. Echocardiography revealed a patent foramen ovale and an aneurysm of the atrial septum protruding into the left atrium, despite normal right atrial pressure. Transesophageal echocardiography showed a prominent Eustachian valve guiding a blood flow from the inferior vena cava directly onto the atrial septum, thereby pushing open the patent foramen ovale. Contrast-enhanced echocardiography confirmed a spontaneous right-to-left shunt through the patent foramen ovale. It was assumed that the platypnea-orthodeoxia was caused by a prominent Eustachian valve redirected to the patent foramen ovale as a result of severe osteoporosis with subsequent thoracic kyphosis and a change in the position of the entire heart. The patient underwent permanent transcatheter closure of the patent foramen ovale after hemodynamic assessment had confirmed a significant right-to-left shunt through it. After the procedure the arterial oxygen pressure increased significantly in the upright position and dyspnea improved

Partitioning of the linear photon momentum in multiphoton ionization

The balance of the linear photon momentum in multiphoton ionization is studied experimentally. In the experiment argon and neon atoms are singly ionized by circularly polarized laser pulses with a wavelength of 800 nm and 1400 nm in the intensity range of 10^{14} - 10^{15} W/cm^2. The photoelectrons are measured using velocity map imaging. We find that the photoelectrons carry linear momentum corresponding to the photons absorbed above the field free ionization threshold. Our finding has implications for concurrent models of the generation of terahertz radiation in filaments.Comment: 4 pages, 3 figure

Sustainable Agriculture for Alaska and the Circumpolar North: Part III. Meeting the Challenges of High-Latitude Farming

Agriculture is a severely underdeveloped industry in Alaska and throughout most of the Subarctic. Growers and entrepreneurs must overcome a diverse set of challenges to achieve greater sustainability in northern communities where resilience is threatened by food insecurity and challenges to northern agriculture have limited the industry. However, several field-based or social policy solutions to problems of high-latitude agriculture have been proposed or are being put into practice. Field-based solutions include the use of special infrastructure or farm management strategies to extend the short growing season, improve soil quality, integrate appropriate pest and irrigation management practices, and further develop the livestock sector. Social and policy solutions are resolutions or decisions reached by stakeholders and government, often through cooperative interaction and discussion. These solutions stem from meaningful discussion and decision making among community members, organizations, agencies, and legislators. Social and policy solutions for Alaska include addressing the high costs of land and the preservation of agricultural lands; improved markets and market strategies; more appropriate funding for research, education and infrastructure; and other integrative or cooperative efforts. Collectively, these solutions will work to improve the outlook for sustainable agriculture in Alaska.En Alaska et dans une grande partie des régions subarctiques, l’agriculture est une industrie extrêmement sous-développée. Les producteurs et les entrepreneurs doivent surmonter un ensemble de défis variés pour donner lieu à une plus grande durabilité dans les collectivités nordiques, là où la résilience est menacée par l’insécurité alimentaire et où les défis caractérisant l’agriculture nordique imposent des restrictions à l’industrie. Cependant, plusieurs solutions apportées sur le terrain ou par le biais de politiques sociales vis-à-vis des problèmes touchant l’agriculture en haute latitude ont été proposées ou sont en train d’être mises en pratique. Parmi les solutions apportées sur le terrain, notons le recours à une infrastructure particulière ou à des stratégies de gestion agricole visant à prolonger la courte saison de croissance, à améliorer la qualité du sol, à intégrer des méthodes de gestion de l’irrigation et des organismes nuisibles, et à mettre davantage l’accent sur le secteur de l’élevage du bétail. Les solutions en matière de politiques sociales prennent la forme de résolutions ou de décisions prises par les parties prenantes et le gouvernement, souvent en collaboration et à la lumière de discussions. Ces solutions découlent de discussions et de prises de décisions importantes entre les membres des collectivités, les organisations, les agences et les législateurs. Les solutions de politiques sociales de l’Alaska portent notamment sur le coût élevé de la terre et la conservation des terres agricoles, sur l’amélioration des marchés et des stratégies de commercialisation, sur la nécessité d’obtenir des sources de financement plus adéquates pour la recherche, l’éducation et l’infrastructure, ainsi que sur d’autres efforts d’intégration et de coopération. Ensemble, ces solutions permettront d’améliorer la conjoncture de l’agriculture durable en Alaska

Sustainable Agriculture for Alaska and the Circumpolar North: Part II. Environmental, Geophysical, Biological and Socioeconomic Challenges

Local agriculture, food security and food supply are limited in Alaska, as well as in much of the circumpolar North. These limitations stem from a suite of challenges that have never been well characterized, categorized, or wholly defined. We identify these challenges as being environmental, geophysical, biological, or socioeconomic in nature, noting that some challenges are interrelated. Additionally, Alaska is expansive, and growing conditions are highly variable across different regions and microclimates of the state. Environmental challenges to Alaskan agriculture are generally linked to high latitude and include strong seasonality, a short growing season, cold temperatures, and unpredictable frosts. Geophysical challenges are characterized by a high percentage of soils that are wet and cold or low in natural fertility. Biological challenges include cultivar adaptability and selection; the control of various pests, weeds, and diseases; and decreased microbial activity in cold soils, which can allow pesticides to linger and slow mineralization of organic fertilizers. Socioeconomic challenges to farming in Alaska are especially limiting and may categorically represent the strongest hindrances to agriculture. They often overlap or interact with many of the identified agro-ecological and biogeographic challenges. Major socioeconomic issues can be a relatively low financial incentive or reward for farmers; inconsistent or limited markets; the high cost of land, infrastructure, and inputs; zoning challenges; a lack of cooperatives; and for rural farmers, time conflicts with more traditional means of subsistence food acquisition. These challenges collectively represent factors that limit agriculture in Alaska, and they provide a basis and justification for developing more sustainable solutions. agriculture; Alaska; challenges; climate; circumpolar; farming; soils; subarctic; sustainable; socioeconomicEn Alaska, l’agriculture locale, la sécurité alimentaire et les approvisionnements en vivres sont limités. C’est également le cas d’une grande partie du Nord circumpolaire. Ces limitations découlent d’un ensemble de défis qui n’ont jamais été bien caractérisés, catégorisés ou entièrement définis. Nous estimons que ces défis sont d’ordre environnemental, géophysique, biologique ou socioéconomique, et que certains des défis sont interreliés. De plus, l’Alaska est d’une grande étendue, et les conditions de croissance varient énormément d’une région à l’autre et d’un microclimat à l’autre de l’État. De manière générale, les défis environnementaux inhérents à l’agriculture alaskienne ont trait à la haute latitude, ce qui comprend une importante saisonnalité, une courte saison de croissance, des températures froides et des gelées imprévisibles. Pour leur part, les défis géophysiques sont caractérisés par un fort pourcentage de sols humides et froids, ou encore, de sols dont la fertilité naturelle est faible, puis les défis d’ordre biologique ont trait à l’adaptabilité et à la sélection des cultivars, à la lutte contre divers organismes nuisibles, les mauvaises herbes et les maladies, ainsi qu’à une activité microbienne réduite dans les sols froids, ce qui permet aux pesticides de rester plus longtemps et ralentit la minéralisation des engrais organiques. Quant aux défis de nature socioéconomique, ils imposent des restrictions particulièrement fortes en Alaska, au point où ils pourraient même catégoriquement représenter le plus grand obstacle à l’agriculture. Dans bien des cas, les défis se chevauchent ou ont une action réciproque sur un grand nombre d’enjeux agroécologiques et biogéographiques. De plus, les grands enjeux socioéconomiques peuvent prendre la forme de récompenses financières relativement faibles pour les agriculteurs, de marchés irréguliers ou limités, du coût élevé de la terre, des infrastructures et des intrants, d’obstacles inhérents au zonage, d’un manqué de coopératives et, dans le cas des agriculteurs ruraux, de conflits d’emploi du temps avec les moyens de subsistance plus traditionnels d’acquisition de la nourriture. Collectivement, ces défis représentent les facteurs qui imposent des restrictions à l’agriculture en Alaska, et ils constituent les fondements et la justification nécessaires au développement de solutions plus durables

The structure of causal sets

More often than not, recently popular structuralist interpretations of physical theories leave the central concept of a structure insufficiently precisified. The incipient causal sets approach to quantum gravity offers a paradigmatic case of a physical theory predestined to be interpreted in structuralist terms. It is shown how employing structuralism lends itself to a natural interpretation of the physical meaning of causal sets theory. Conversely, the conceptually exceptionally clear case of causal sets is used as a foil to illustrate how a mathematically informed rigorous conceptualization of structure serves to identify structures in physical theories. Furthermore, a number of technical issues infesting structuralist interpretations of physical theories such as difficulties with grounding the identity of the places of highly symmetrical physical structures in their relational profile and what may resolve these difficulties can be vividly illustrated with causal sets.Comment: 19 pages, 4 figure

A new instrument to measure high value, cost-conscious care attitudes among healthcare stakeholders: Development of the MHAQ

Background: Residents have to learn to provide high value, cost-conscious care (HVCCC) to counter the trend of excessive healthcare costs. Their learning is impacted by individuals from different stakeholder groups within the workplace environment. These individuals' attitudes toward HVCCC may influence how and what residents learn. This study was carried out to develop an instrument to reliably measure HVCCC attitudes among residents, staff physicians, administrators, and patients. The instrument can be used to assess the residency-training environment. Method: The Maastricht HVCCC Attitude Questionnaire (MHAQ) was developed in four phases. First, we conducted exploratory factor analyses using original data from a previously published survey. Next, we added nine items to strengthen subscales and tested the new questionnaire among the four stakeholder groups. We used exploratory factor analysis and Cronbach's alphas to define subscales, after which the final version of the MHAQ was constructed. Finally, we used generalizability theory to determine the number of respondents (residents or staff physicians) needed to reliably measure a specialty attitude score. Results: Initial factor analysis identified three subscales. Thereafter, 301 residents, 297 staff physicians, 53 administrators and 792 patients completed the new questionnaire between June 2017 and July 2018. The best fitting subscale composition was a three-factor model. Subscales were defined as high-value care, cost incorporation, and perceived drawbacks. Cronbach's alphas were between 0.61 and 0.82 for all stakeholders on all subscales. Sufficient reliability for assessing national specialty attitude (G-coefficient > 0.6) could be achieved from 14 respondents. Conclusions: The MHAQ reliably measures individual attitudes toward HVCCC in different stakeholders in health care contexts. It addresses key dimensions of HVCCC, providing content validity evidence. The MHAQ can be used to identify frontrunners of HVCCC, pinpoint aspects of residency training that need improvement, and benchmark and compare across specialties, hospitals and regions