2,098 research outputs found
Reading Historic Sites : Interpretive Strategies at Literary House-Museums
This study examines interpretive strategies at house-museums with literary significance, and evaluates how the concept of the house as a readable textâas a social document of traces of past lifeâis balanced with the idea of a literary historic house as a place to interpret humanistic themes explored or embodied by the literary figures commemorated at the site. The three sites examined are the Emily Dickinson Museum in Amherst, MA; the Edgar Allan Poe National Historic Site in Philadelphia, PA; and the Rosenbach Museum and Library in Philadelphia. The basis for evaluation was an analysis of the following aspects of house interpretation: the presentation of the interior, including furnishings and collections; guided tours; other interpretive tools such as written materials available to visitors on site; and exhibits and other program activities. The house-museums in this study attempt to balance the text of domestic life with the literary legacy of the houseâs former inhabitants. The success of each of the three sites depends on their ability to abstract from the material reality of a house the broader humanistic themes that can be found in the recollection of individual lives and in our collective literary tradition
Photoassociation adiabatic passage of ultracold Rb atoms to form ultracold Rb_2 molecules
We theoretically explore photoassociation by Adiabatic Passage of two
colliding cold ^{85}Rb atoms in an atomic trap to form an ultracold Rb_2
molecule. We consider the incoherent thermal nature of the scattering process
in a trap and show that coherent manipulations of the atomic ensemble, such as
adiabatic passage, are feasible if performed within the coherence time window
dictated by the temperature, which is relatively long for cold atoms. We show
that a sequence of ~2*10^7 pulses of moderate intensities, each lasting ~750
ns, can photoassociate a large fraction of the atomic ensemble at temperature
of 100 microkelvin and density of 10^{11} atoms/cm^3. Use of multiple pulse
sequences makes it possible to populate the ground vibrational state. Employing
spontaneous decay from a selected excited state, one can accumulate the
molecules in a narrow distribution of vibrational states in the ground
electronic potential. Alternatively, by removing the created molecules from the
beam path between pulse sets, one can create a low-density ensemble of
molecules in their ground ro-vibrational state.Comment: RevTex, 23 pages, 9 figure
Antibiotics in early life and childhood pre-B-ALL. Reasons to analyze a possible new piece in the puzzle
Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer with precursor B-cell ALL (pB-ALL) accounting for~85% of the cases. Childhood pB-ALL development is infuenced by genetic susceptibility and host immune
responses. The role of the intestinal microbiome in leukemogenesis is gaining increasing attention since Vicente-Dueñasâ
seminal work demonstrated that the gut microbiome is distinct in mice genetically predisposed to ALL and that the alteration of this microbiome by antibiotics is able to trigger pB-ALL in Pax5 heterozygous mice in the absence of infectious
stimuli. In this review we provide an overview on novel insights on the role of the microbiome in normal and preleukemic hematopoiesis, infammation, the efect of dysbiosis on hematopoietic stem cells and the emerging importance of
the innate immune responses in the conversion from preleukemic to leukemic state in childhood ALL. Since antibiotics,
which represent one of the most widely used medical interventions, alter the gut microbial composition and can cause a
state of dysbiosis, this raises exciting epidemiological questions regarding the implications for antibiotic use in early life,
especially in infants with a a preleukemic âfrst hitâ. Sheading light through a rigorous study on this piece of the puzzle
may have broad implications for clinical practice
Holocene changes in African vegetation: tradeoff between climate and water availability
Although past climate change is well documented in West Africa through
instrumental records, modeling activities, and paleo-data, little is known
about regional-scale ecosystem vulnerability and long-term impacts of climate
on plant distribution and biodiversity. Here we use paleohydrological and
paleobotanical data to discuss the relation between available surface water,
monsoon rainfall and vegetation distribution in West Africa during the
Holocene. The individual patterns of plant migration or community shifts in
latitude are explained by differences among tolerance limits of species to
rainfall amount and seasonality. Using the probability density function
methodology, we show here that the widespread development of lakes, wetlands
and rivers at the time of the "Green Sahara" played an additional role in
forming a network of topographically defined water availability, allowing for
tropical plants to migrate north from 15 to 24° N (reached ca.
9 cal ka BP). The analysis of the spatioâtemporal changes in
biodiversity, through both pollen occurrence and richness, shows that the
core of the tropical rainbelt associated with the Intertropical Convergence
Zone was centered at 15â20° N during the early Holocene wet period,
with comparatively drier/more seasonal climate conditions south of
15° N
Structure and nature of ice XIX
Ice is a material of fundamental importance for a wide range of scientific disciplines including physics, chemistry, and biology, as well as space and materials science. A well-known feature of its phase diagram is that high-temperature phases of ice with orientational disorder of the hydrogen-bonded water molecules undergo phase transitions to their ordered counterparts upon cooling. Here, we present an example where this trend is broken. Instead, hydrochloric-acid-doped ice VI undergoes an alternative type of phase transition upon cooling at high pressure as the orientationally disordered ice remains disordered but undergoes structural distortions. As seen with in-situ neutron diffraction, the resulting phase of ice, ice XIX, forms through a Pbcn-type distortion which includes the tilting and squishing of hexameric clusters. This type of phase transition may provide an explanation for previously observed ferroelectric signatures in dielectric spectroscopy of ice VI and could be relevant for other icy materials
One-Dimensional Arsenic Allotropes: Polymerization of Yellow Arsenic Inside Single-Wall Carbon Nanotubes
The pnictogen nanomaterials, including phosphorene and arsenene, display remarkable electronic and chemical properties. Yet, the structural diversity of these main group elements is still poorly explored. Here we fill singleâwall carbon nanotubes with elemental arsenic from the vapor phase. Using electron microscopy, we find chains of highly reactive As4 molecules as well as two new oneâdimensional allotropes of arsenic: a singleâstranded zigâzag chain and a doubleâstranded zigâzag ladder. These linear structures are important intermediates between the gasâphase clusters of arsenic and the extended sheets of arsenene. Raman spectroscopy indicates weak electronic interaction between the arsenic and the nanotubes which implies that the formation of the new allotropes is driven primarily by the geometry of the confinement. The relative stabilities of the new arsenic structures are estimated computationally. Bandâgap calculations predict that the insulating As4 chains become semiconducting, once converted to the zigâzag ladder, and form a fully metallic allotrope of arsenic as the zigâzag chain
Preparation and Structure of the Ion-Conducting Mixed Molecular Glass Ga2I3.17
Modern functional glasses have been prepared from a wide range of precursors, combining the benefits of their isotropic disordered structures with the innate functional behavior of their atomic or molecular building blocks. The enhanced ionic conductivity of glasses compared to their crystalline counterparts has attracted considerable interest for their use in solid-state batteries. In this study, we have prepared the mixed molecular glass Ga2I3.17 and investigated the correlations between the local structure, thermal properties, and ionic conductivity. The novel glass displays a glass transition at 60 °C, and its molecular make-up consists of GaI4â tetrahedra, Ga2I62â heteroethane ions, and Ga+ cations. Neutron diffraction was employed to characterize the local structure and coordination geometries within the glass. Raman spectroscopy revealed a strongly localized nonmolecular mode in glassy Ga2I3.17, coinciding with the observation of two relaxation mechanisms below Tg in the AC admittance spectra
Detailed crystallographic analysis of the ice V to ice XIII hydrogen-ordering phase transition
Ice V is a structurally highly complex material with 28 water molecules in its monoclinic unit cell. It is classified as a hydrogen-disordered phase of ice. Yet, some of its hydrogen-bonded water molecules display significant orientational order. Upon cooling pure ice V, additional orientational ordering cannot be achieved on the experimental time scale. Doping with hydrochloric acid has been shown to be most effective in enabling the phase transition of ice V to its hydrogen-ordered counterpart ice XIII. Here, we present a detailed crystallographic study of this phase transition investigating the effects of hydrochloric and hydrofluoric acid as well as lithium and potassium hydroxide doping. The magnitudes of the stepwise changes in the lattice constants during the phase transition are found to be more sensitive indicators for the extent of hydrogen order in ice XIII than the appearance of new Bragg peaks. Hydrofluoric acid and lithium hydroxide doping enable similar ordering processes as hydrochloric acid but with slower kinetics. The various possible space groups and ordered configurations of ice XIII are examined systematically, and the previously determined P21/a structure is confirmed. Interestingly, the partial hydrogen order already present in ice V is found to perpetuate into ice XIII, and these ordering processes are found to be independent of pressure. Overall, the hydrogen ordering goes along with a small increase in volume, which appears to be the origin of the slower hydrogen-ordering kinetics under pressure. Heating pressure-quenched samples at ambient pressure revealed low-temperature "transient ordering" features in both diffraction and calorimetry
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