Cardiac T2 measurements in patients with iron overload: a comparison of imaging parameters and analysis techniques

Measurement of cardiac T2 has emerged as an important tool to noninvasively quantify cardiac iron concentration in order to detect preclinical evidence of toxic levels and titrate chelation therapy. However, there exists variation among practitioners in cardiac T2 measurement methods. This study examines the impact of different imaging parameters and data analysis techniques on the calculated cardiac R2 (1/T2) in patients at risk for cardiac siderosis. The study group consisted of 36 patients with thalassemia syndromes who had undergone clinical magnetic resonance imaging assessment of cardiac siderosis using a standardized protocol and who were selected to yield a broad range of cardiac R2 values. Cardiac R2 measurements were performed on a 1.5-T scanner using an electrocardiogram-gated, segmented, multiecho gradient echo sequence obtained in a single breath-hold. R2 was calculated from the signal intensity versus echo time data in the ventricular septum on a single midventricular short-axis slice. There was good agreement between R2 measured with a blood suppression prepulse (black blood technique) and without (mean difference 6.0 ± 10.7 Hz). The black blood technique had superior within-study reproducibility (R2 mean difference 1.6 ± 8.6 Hz versus 2.7 ± 14.6 Hz) and better interobserver agreement (R2 mean difference 3.4 ± 8.2 Hz versus 8.3 ± 16.5 Hz). With the same minimum echo time, the use of small (1.0 ms) versus large (2.2 ms) echo spacing had minimal impact on cardiac R2 (mean difference 0.3 ± 8.7 Hz). The application of a region-of-interest-based versus a pixel-based data analysis also had little effect on cardiac R2 calculation (mean difference 8.4 ± 6.9 Hz). With black blood images, fitting the signal curve to a monoexponential decay or to a monoexponential decay with a constant offset yielded similar R2 values (mean difference 3.4 ± 8.1 Hz). In conclusion, the addition of a blood suppression prepulse for cardiac R2 measurement yields similar R2 values and improves reproducibility and interobserver agreement. The findings regarding other variations may be helpful in establishing a broadly accepted imaging and analysis technique for cardiac R2 calculation.     

Modelling the size and skill-mix of hospital nursing teams

Previously published work has described the development of a hospital capacity simulation tool, PROMPT. PROMPT has now been adopted by a number of hospitals in the UK and is used for both strategic and operational planning and management of key hospital resources. The work, as presented here, extends the PROMPT functionality to consider in more detail workforce issues. In particular, working with some of the current hospital users, the research has focussed on detailed planning for calculating the size and skill-mix of inpatient nursing teams. The chosen methodology utilizes both simulation and optimization. Outputs from the PROMPT three-phase discrete event simulation are fed into a stochastic programme which suggests the optimal number of nurses to employ (whole time equivalents) by skill-mix and the corresponding numbers by shift. A novel feature of the tool is the ability to predict and compare nursing needs based on different methods of capturing patient-to-nurse ratios as currently adopted across the UK National Health Service. Illustrative results from one hospital demonstrate that although the overall sizes of nursing teams on different wards are of an acceptable level and comparable to the outputs from the simulation phase of the work, often the number of nurses employed at different grades is not well matched to patient needs and the skill-mix should be reconsidered. Results from the optimization phase of the work suggest that it is cost beneficial to increase the number of permanently employed nurses to account for fluctuations in demand and corresponding high costs of temporary (agency) nurses. The scenario functionality of the tool permits for the study of changing size and skill-mix as a consequence of changes in patient volumes, patient case-mix, numbers of beds and length of stay.     

Efficient and effective heuristics for the coordinated capacitated lot-size problem

Coordinating procurement decisions for a family of products that share a constrained resource, such as an ocean shipping container, is an important managerial problem. However due to the problem’s difficult mathematical properties, efficient and effective solution procedures for the problem have eluded researchers. This paper proposes two heuristics, for the capacitated, coordinated dynamic demand lot-size problem with deterministic but time-varying demand. In addition to inventory holding costs, the problem assumes a joint setup cost each time any member of the product family is replenished and an individual item setup cost for each item type replenished. The objective is to meet all customer demand without backorders at minimum total cost. We propose a six-phase heuristic (SPH) and a simulated annealing meta-heuristic (SAM). The SPH begins by assuming that each customer demand is met by a unique replenishment and then it seeks to iteratively maximize the net savings associated with order consolidation. Using SPH to find a starting solution, the SAM orchestrates escaping local solutions and exploring other areas of the solution state space that are randomly generated in an annealing search process. The results of extensive computational experiments document the effectiveness and efficiency of the heuristics. Over a wide range of problem parameter values, the SPH and SAM find solutions with an average optimality gap of 1.53% and 0.47% in an average time of 0.023 CPU seconds and 0.32 CPU seconds, respectively. The heuristics are strong candidates for application as stand alone solvers or as an upper bounding procedure within an optimization based algorithm. The procedures are currently being tested as a solver in the procurement software suite of a nationally recognized procurement software provider.     

α-Diimine Ligand Coordination and C–H Bond Activation in the Reaction of Os3(CO)10(MeCN)2 with 6-R-2,2′-Bipyridine (where R?=?Et, Ph): X-ray Diffraction Structures of the Ortho-Metalated Hydride Clusters HOs3(CO)9(N2C10H6-6-R)

Abstract  

The reactivity of the labile cluster Os₃(CO)₁₀(MeCN)₂ (1) with the monofunctionalized heterocyclic ligands 6-R-2,2′-bipyridine (where R = Et, Ph) has been investigated. The alkyl-substituted heterocycle 6-Et-2,2′-bipyridine reacts with 1 in refluxing CH₂Cl₂ to give an isomeric mixture of HOs₃(CO)₉(N₂C₁₂H₁₁) due to cyclometalation of the side-chain ethyl group (2) and ortho metalation of the unsubstituted bipyridine ring (3). The solid-state structure of the latter cluster, HOs₃(CO)₉(N₂C₁₀H₆-6-Et) (3), has unequivocally established the site of the C-H bond activation in the product. Treatment of 1 with the aryl-substituted ligand 6-Ph-2,2′-bipyridine proceeds similarly with ortho metalation at the ancillary phenyl group and the C-6′ ortho site of the unsubstituted bipyridine ring, as verified by ¹H NMR spectroscopy. The X-ray diffraction structure of the thermodynamically more stable bipyridine-metalated cluster HOs₃(CO)₉(N₂C₁₀H₆-6-Ph) (5) has been determined. The course of these reactions is discussed with respect to our recent study involving the reaction of cluster 1 with the ligand 6-Me-2,2′-bipyridine.     

A sharp Balian–Low uncertainty principle for shift-invariant spaces

A sharp version of the Balian–Low theorem is proven for the generators of finitely generated shift-invariant spaces. If generators ${\{f_k\}}_{k=1}^K?L^2({\mathbb{R}}^d)$ are translated along a lattice to form a frame or Riesz basis for a shift-invariant space V, and if V has extra invariance by a suitable finer lattice, then one of the generators $f_k$ must satisfy ${\int }_{{\mathbb{R}}^d}|x||f_k(x){|}^{2}dx=\infty$, namely, $\stackrel{?}{f_k}?H^{1/2}({\mathbb{R}}^d)$. Similar results are proven for frames of translates that are not Riesz bases without the assumption of extra lattice invariance. The best previously existing results in the literature give a notably weaker conclusion using the Sobolev space $H^{d/2+?}({\mathbb{R}}^d)$; our results provide an absolutely sharp improvement with $H^{1/2}({\mathbb{R}}^d)$. Our results are sharp in the sense that $H^{1/2}({\mathbb{R}}^d)$ cannot be replaced by $H^s({\mathbb{R}}^d)$ for any $s<1/2$.     

Alternative dual frames for digital-to-analog conversion in sigma–delta quantization

We design alternative dual frames for linearly reconstructing signals from sigma–delta (ΣΔ) quantized finite frame coefficients. In the setting of sampling expansions for bandlimited functions, it is known that a stable rth order sigma–delta quantizer produces approximations where the approximation error is at most of order 1 / λ ^r , and λ > 1 is the oversampling ratio. We show that the counterpart of this result is not true for several families of redundant finite frames for \mathbbR^d\mathbb{R}^d when the canonical dual frame is used in linear reconstruction. As a remedy, we construct alternative dual frame sequences which enable an rth order sigma–delta quantizer to achieve approximation error of order 1/N ^r for certain sequences of frames where N is the frame size. We also present several numerical examples regarding the constructions.     

Erratum to: Sobolev Duals in Frame Theory and Sigma-Delta Quantization

A new class of alternative dual frames is introduced in the setting of finite frames for ℝ ^d . These dual frames, called Sobolev duals, provide a high precision linear reconstruction procedure for Sigma-Delta (ΣΔ) quantization of finite frames. The main result is summarized as follows: reconstruction with Sobolev duals enables stable rth order Sigma-Delta schemes to achieve deterministic approximation error of order O(N^-r)\mathcal{O}(N^{-r}) for a wide class of finite frames of size N. This asymptotic order is generally not achievable with canonical dual frames. Moreover, Sobolev dual reconstruction leads to minimal mean squared error under the classical white noise assumption.     

The magnetic circular dichroism spectrum of matrix-isolated TaO

TaO has been matrix-isolated in an argon matrix at 14 K and 24 K and studied spectroscopically in the visible region (300–850 nm). Both adsorption and magnetic circular dichroism (MCD) spectra have been recorded and analyzed. A determination of the total angular momentum quantum numbers (ω) for fourteen excited electronic states has been made. The g factors for the ground ²Δ_{$\text{3}\text{2}$} and excited ²φ_{$\text{5}\text{2}$} states have been determined from a moment analysis of the MCD and absorption spectra of the 450.3 nm band. The present study indicates the power of the combination of magnetic circular dichroism and matrix isolation for the assignment of excited electronic states of high temperature molecules.     

Dynamic fleet management as a logistics queueing network

This paper introduces a new framework for modeling and solving dynamic fleet management problems, which we call the Logistics Queueing Network (LQN). A variety of problems in logistics involve the combined problem of moving freight from origin to destination while simultaneously managing the capacity required to move this freight. Standard formulations for real-world problems usually lead to intractably large linear programs. The LQN approach can take into account more real-world detail and is considerably faster than classical LP formulations. The solutions generated using the LQN approach are shown to be within a few percentage points of the LP optimal solutions depending on the size of the capacity fleets.