Highly resolved measurements of Stark-tuned Förster resonances between Rydberg atoms.

We report on experiments exploring Stark-tuned Förster resonances between Rydberg atoms with high resolution in the Förster defect. The individual resonances are expected to exhibit different angular dependencies, opening the possibility to tune not only the interaction strength but also the angular dependence of the pair state potentials by an external electric field. We achieve a high resolution by optical Ramsey interferometry for Rydberg atoms combined with electric field pulses. The resonances are detected by a loss of visibility in the Ramsey fringes due to resonances in the interaction. We present measurements of the density dependence as well as of the coherence time at and close to Förster resonances.

Rydberg trimers and excited dimers bound by internal quantum reflection.

In a combined experimental and theoretical effort we report on two novel types of ultracold long-range Rydberg molecules. First, we demonstrate the creation of triatomic molecules of one Rydberg atom and two ground-state atoms in a single-step photoassociation. Second, we assign a series of excited dimer states that are bound by a so far unexplored mechanism based on internal quantum reflection at a steep potential drop. The properties of the Rydberg molecules identified in this work qualify them as prototypes for a new type of chemistry at ultracold temperatures.

Creation of two tomographic voxel models of paediatric patients in the first year of life.

Tomographic computational models, based on regional segmentation of CT or MRI medical images, have increasingly been proposed as replacements for current stylized mathematical models of human anatomy used in radiation dosimetry studies. While much effort has been devoted towards the creation of adult models, few research studies have been initiated to address the need for models supporting paediatric radiology dosimetry. In this study, two tomographic models were created using a combination of automatic and manual segmentation via a program created in-house using IDL version 5.5. The first model is of a normal 6 day female newborn, and consists of a 512 x 512 x 485 data array. The CT slices of this model were obtained every 1 mm, and 66 different anatomic regions were defined. The second model is of a patient developmentally equivalent to a 2 month male, and was saved as a 512 x 512 x 438 data array. This subject had severe tissue oedema within the gut, kidneys, liver and spleen. The model is thus considered representative of a critically ill child, from a patient subpopulation expected to receive a larger than normal number of diagnostic x-ray exams. The voxel volumes for the two models are 0.35 mm3 and 0.30 mm3, respectively, thus making these models the most detailed in existence for paediatric dosimetry applications. Ratios of organ masses for the UF newborn model to those within the reference ORNL/MIRD model range from highs of 1.2 to 1.7 for the oesophagus and small intestine/colon, respectively, to lows of 0.18 to 0.27 for the mandible and humeri, respectively. For the UF 2 month model, ratios of organ masses in the UF model to those in the 8 week GSF BABY model ranged from highs of 3.7 to 5.2 for the clavicles and spleen, respectively, to lows of 0.2 to 0.3 for the adrenals and scapulae, respectively.

A comparison of newborn stylized and tomographic models for dose assessment in paediatric radiology.

Establishment of organ doses from diagnostic and interventional examinations is a key component to quantifying the radiation risks from medical exposures and for formulating corresponding dose-reduction strategies. Radiation transport models of human anatomy provide a convenient method for simulating radiological examinations. At present, two classes of models exist: stylized mathematical models and tomographic voxel models. In the present study, organ dose comparisons are made for projection radiographs of both a stylized and a tomographic model of the newborn patient. Sixteen separate radiographs were simulated for each model at x-ray technique factors typical of newborn examinations: chest, abdomen, thorax and head views in the AP, PA, left LAT and right LAT projection orientation. For AP and PA radiographs of the torso (chest, abdomen and thorax views), the effective dose assessed for the tomographic model exceeds that for the stylized model with per cent differences ranging from 19% (AP abdominal view) to 43% AP chest view. In contrast, the effective dose for the stylized model exceeds that for the tomographic model for all eight lateral views including those of the head, with per cent differences ranging from 9% (LLAT chest view) to 51% (RLAT thorax view). While organ positioning differences do exist between the models, a major factor contributing to differences in effective dose is the models' exterior trunk shape. In the tomographic model, a more elliptical shape is seen thus providing for less tissue shielding for internal organs in the AP and PA directions, with corresponding increased tissue shielding in the lateral directions. This observation is opposite of that seen in comparisons of stylized and tomographic models of the adult.

A homonuclear molecule with a permanent electric dipole moment.

Permanent electric dipole moments in molecules require a breaking of parity symmetry. Conventionally, this symmetry breaking relies on the presence of heteronuclear constituents. We report the observation of a permanent electric dipole moment in a homonuclear molecule in which the binding is based on asymmetric electronic excitation between the atoms. These exotic molecules consist of a ground-state rubidium (Rb) atom bound inside a second Rb atom electronically excited to a high-lying Rydberg state. Detailed calculations predict appreciable dipole moments on the order of 1 Debye, in excellent agreement with the observations.

Functional platelets after storage in vitro for 15--21 days.

Blood platelets are notoriously difficult to preserve in vitro for long periods of time. Despite many efforts to solve the problem and improve conditions for storage, platelets lose their ability to respond to aggregating agents after 72--96 hours and are routinely discarded by blood banks after three days if not used for transfusion. The present study has evaluated the influence of raising the pH of the anticoagulant used to collect blood on the functional viability of platelets during storage at room temperature. Twenty-four samples of C-PRP were followed for 15 days and 12 samples for 21 days. Although platelet counts fell steadily during the 3-week storage period, a significant proportion of the cells remained viable. After 5--10 days the platelets responded as well to threshold concentrations of ADP and sodium arachidonate (SA) as on Day 0, and reactions to the same agents on Day 15 were nearly as impressive. Even on Day 21, responses to ADP and SA could still be elicited. Biochemical studies on samples stored for 15--21 days revealed normal levels of serotonin after 2 weeks and a fall of less than 30% after 3 weeks. The ability of the cells to convert 14C-arachidonic acid into thromboxane B2 was well maintained over the 3-week period. Adenine nucleotide levels fell 25% over 15 days and over 50% by 21 days, but the capacity of the cells to take up 14C-adenine and convert it to AMP, ADP, and ATP was increased, and ATP/ADP ratios were not greatly different from those on Day 0. Physical changes were apparent in most platelets by Day 15. However, 5--20% of platelets in 15--21-day-old samples were discoid in shape and contained circumferential bands of microtubules and small amounts of glycogen. The findings suggest that high pH during collection of blood, preparation of C-PRP, and early phases of storage may foster long-term preservation of viable platelets in vitro.