582 research outputs found
Reinstated episodic context guides sampling-based decisions for reward.
How does experience inform decisions? In episodic sampling, decisions are guided by a few episodic memories of past choices. This process can yield choice patterns similar to model-free reinforcement learning; however, samples can vary from trial to trial, causing decisions to vary. Here we show that context retrieved during episodic sampling can cause choice behavior to deviate sharply from the predictions of reinforcement learning. Specifically, we show that, when a given memory is sampled, choices (in the present) are influenced by the properties of other decisions made in the same context as the sampled event. This effect is mediated by fMRI measures of context retrieval on each trial, suggesting a mechanism whereby cues trigger retrieval of context, which then triggers retrieval of other decisions from that context. This result establishes a new avenue by which experience can guide choice and, as such, has broad implications for the study of decisions
Extraordinary epitaxial alignment of graphene islands on Au(111)
Pristine, single-crystalline graphene displays a unique collection of
remarkable electronic properties that arise from its two-dimensional, honeycomb
structure. Using in-situ low-energy electron microscopy, we show that when
deposited on the (111) surface of Au carbon forms such a structure. The
resulting monolayer, epitaxial film is formed by the coalescence of dendritic
graphene islands that nucleate at a high density. Over 95% of these islands can
be identically aligned with respect to each other and to the Au substrate.
Remarkably, the dominant island orientation is not the better lattice-matched
30^{\circ} rotated orientation but instead one in which the graphene [01] and
Au [011] in-plane directions are parallel. The epitaxial graphene film is only
weakly coupled to the Au surface, which maintains its reconstruction under the
slightly p-type doped graphene. The linear electronic dispersion characteristic
of free-standing graphene is retained regardless of orientation. That a weakly
interacting, non-lattice matched substrate is able to lock graphene into a
particular orientation is surprising. This ability, however, makes Au(111) a
promising substrate for the growth of single crystalline graphene films
A WFC3 Grism Emission Line Redshift Catalog in the GOODS-South Field
We combine HST/WFC3 imaging and G141 grism observations from the CANDELS and
3D-HST surveys to produce a catalog of grism spectroscopic redshifts for
galaxies in the CANDELS/GOODS-South field. The WFC3/G141 grism spectra cover a
wavelength range of 1.1<lambda<1.7 microns with a resolving power of R~130 for
point sources, thus providing rest-frame optical spectra for galaxies out to
z~3.5. The catalog is selected in the H-band (F160W) and includes both galaxies
with and without previously published spectroscopic redshifts. Grism spectra
are extracted for all H-band detected galaxies with H<24 and a CANDELS
photometric redshift z_phot > 0.6. The resulting spectra are visually inspected
to identify emission lines and redshifts are determined using cross-correlation
with empirical spectral templates. To establish the accuracy of our redshifts,
we compare our results against high-quality spectroscopic redshifts from the
literature. Using a sample of 411 control galaxies, this analysis yields a
precision of sigma_NMAD=0.0028 for the grism-derived redshifts, which is
consistent with the accuracy reported by the 3D-HST team. Our final catalog
covers an area of 153 square arcmin and contains 1019 redshifts for galaxies in
GOODS-S. Roughly 60% (608/1019) of these redshifts are for galaxies with no
previously published spectroscopic redshift. These new redshifts span a range
of 0.677 < z < 3.456 and have a median redshift of z=1.282. The catalog
contains a total of 234 new redshifts for galaxies at z>1.5. In addition, we
present 20 galaxy pair candidates identified for the first time using the grism
redshifts in our catalog, including four new galaxy pairs at z~2, nearly
doubling the number of such pairs previously identified.Comment: 25 Pages, 9 Figures, submitted to A
MEN I pancreas: A histological and immunohistochemical study
The spectrum and extent of islet cell histopathological findings in patients with multiple endocrine neoplasia, type I (MEN I) syndrome has never been clearly defined. Although some patients have discreet tumors causing clinically evident syndromes, others may have no symptoms until metastatic islet cell carcinoma is apparent. Whether diffuse islet cell disease occurs in all patients with grossly apparent tumors is not known. This study is an attempt to define both the functional and anatomical extent of islet cell disease and its relationship with the clinical course of patients with MEN I syndrome. The resected specimens of pancreas from 14 patients with MEN I syndrome were evaluated for hyperplasia, nesidioblastosis, multiple tumors, and evidence of malignancy. In 12 cases, specimens consisted of distal pancreas and, in 2 cases, the entire pancreas was available. Multiple sections were taken from each specimen. Immunoperoxidase staining was done for gastrin, pancreatic polypeptide, glucagon, serotonin, VIP, somatostatin, and neuron-specific enolase in sections of 24 tumors from 10 patients. Five of the 10 patients with Zollinger-Ellison syndrome underwent total gastrectomy and 3 others underwent only pancreatic procedures to control their acid hypersecretion. The following is concluded. All MEN I patients with pancreatic neoplasms have diffuse islet cell involvement consisting of nesidioblastosis, micro- and macronodular hyperplasia. Some tumors produce multiple hormones and these patients are at risk to develop new tumors, but complete excision of grossly apparent tumors may result in long-term control of the endocrinopathy present. This is particularly true for patients with insulinoma and hypoglycemia. Selected patients with gastrinoma may also be considered for excision of their islet cell tumor(s) without concomitant gastrectomy, especially if transhepatic venous sampling demonstrates a single site of excess gastrin production. However, if transhepatic venous sampling demonstrates diffuse sources of hypergastrinemia, a local pancreatic procedure will invariably be unsuccessful. Total pancreatectomy in MEN I patients with disease localized to the pancreas is the only curative surgical procedure but is rarely indicated. L'histopathologie des cellules insulaires pancrĂ©atiques des malades qui prĂ©sentent un syndrome MEN I n'a jamais Ă©tĂ© parfaitement dĂ©finie. Si certains parmi eux sont porteurs de petites tumeurs qui se manifestent par des syndromes cliniques patents, d'autres n'accusent aucun symptĂ´me avant que des mĂ©tastases nĂ©oplasiques ne se manifestent. En particulier, on ne sait pas si les altĂ©rations des cellules insulaires sont diffuses quand les malades prĂ©sentent des tumeurs Ă©videntes. Cette Ă©tude a pour but de dĂ©finir Ă la fois l'importance anatomique et l'importance fonctionnelle de la maladie insulaire par rapport Ă son expression clinique chez les sujets concernĂ©s par ce syndrome. Pour ce faire, des spĂ©cimens provenant de 14 malades atteints du syndrome MEN I ont Ă©tĂ© Ă©tudiĂ©s eu Ă©gard Ă l'hyperplasie, Ă la nĂ©sidioblastose, Ă la multiplicitĂ© des Ă®lots tumoraux, Ă la malignitĂ©. Dans 12 cas, les spĂ©cimens rĂ©pondaient au pancrĂ©as distal, dans 2 cas Ă la totalitĂ© du pancrĂ©as. De multiples coupes furent pratiquĂ©es au niveau de chaque pièce soumise Ă l'examen. L'imprĂ©gnation Ă l'immunoperoxidase concerna les coupes de 24 tumeurs provenant de 10 patients. Cinq des 10 malades qui prĂ©sentaient un syndrome de Zollinger-Ellison avaient subi une gastrectomie totale et 3 une intervention pancrĂ©atique pour contrĂ´ler leur hypersĂ©crĂ©tion acide. Les conclusions tirĂ©es de cette Ă©tude furent les suivantes: tous les malades accusant un syndrome MEN I et porteurs d'un nĂ©opolasme pancrĂ©atique prĂ©sentaient des lĂ©sions insulaires diffuses rĂ©pondant Ă une nĂ©sidioblastose, Ă une hyperplasie micronodulaire et macronodulaire. Quelques tumeurs produisaient de multiples hormones: gastrine, polypeptide pancrĂ©atique, glucagon, sĂ©rotonine, V.I.P., somatostatine, testĂ©es par la mĂ©thode. Il rĂ©sulte de ces constatations que les risques de rĂ©cidive tumorale après exĂ©rèse complète des tumeurs Ă©videntes ne sont pas Ă Ă©carter, encore que l'exĂ©rèse permette de contrĂ´ler longtemps l'endocrinopathie. Ceci est particulièrement vrai pour les insulinomes hypoglycĂ©miants. En ce qui concerne les gastrinomes, leur exĂ©rèse peut ĂŞtre suffisante, en particulier lorsque les prĂ©lèvements veineux Ă©tagĂ©s montrent qu'ils sont uniques; la gastrectomie concomitante est alors inutile. En revanche, lorsque la gastrine est trouvĂ©e en excès au niveau de multiples Ă©chantillons veineux, l'exĂ©rèse tumorale est insuffisante et la pancrĂ©atectomie totale reprĂ©sente l'intervention indispensable; en fait, son indication est rare. La variedad del espectro de la histopatologĂa de las cĂ©lulas insulares en pacientes con sindrome de neoplasias endocrinas mĂşltiples tipo I (NEM I) todavĂa no ha sido claramente definido. AĂşn cuando algunos pacientes poseen tumores discretos que causan sĂndromes clĂnicamente evidentes, otros pueden no exhibir sintomatologĂa alguna hasta cuando se hace evidente un carcinoma metastásico de cĂ©lulas insulares. No se sabe si hay enfermedad difusa de las cĂ©lulas insulares en todo paciente con tumores macroscĂłpicamente aparentes, ni además se conoce con quĂ© frecuencia se desarrollan nuevos tumores en pacientes con sĂndrome NEM I despuĂ©s de resecciĂłn local o de pancreatectomĂa parcial para tumores primarios de cĂ©lulas insulares. El presente estudio intenta definir la extensiĂłn funcional y anatĂłmica de la enfermedad de las cĂ©lulas insulares y su relaciĂłn con la evoluciĂłn clĂnica en pacientes con el sĂndrome NEM I.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41313/1/268_2005_Article_BF01654938.pd
Educating a New Generation of Doctors to Improve the Health of Populations in Low- and Middle-Income Countries
Francesca Celletti and colleagues from WHO argue that a transformation in the scale-up of medical education in low- and middle-income countries is needed, and detail what this might look like
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