Positivity in the presence of initial system-environment correlation

The constraints imposed by the initial system-environment correlation can lead to nonpositive Dynamical maps. We find the conditions for positivity and complete positivity of such dynamical maps by using the concept of an assignment map. Any initial system-environment correlations make the assignment map nonpositive, while the positivity of the dynamical map depends on the interplay between the assignment map and the system-environment coupling. We show how this interplay can reveal or hide the nonpositivity of the assignment map. We discuss the role of this interplay in Markovian models.Comment: close to the published version. 5 pages, 1 figur

Reconstructing large-scale structure with neutral hydrogen surveys

Upcoming 21-cm intensity surveys will use the hyperfine transition in emission to map out neutral hydrogen in large volumes of the universe. Unfortunately, large spatial scales are completely contaminated with spectrally smooth astrophysical foregrounds which are orders of magnitude brighter than the signal. This contamination also leaks into smaller radial and angular modes to form a foreground wedge, further limiting the usefulness of 21-cm observations for different science cases, especially cross-correlations with tracers that have wide kernels in the radial direction. In this paper, we investigate reconstructing these modes within a forward modeling framework. Starting with an initial density field, a suitable bias parameterization and non-linear dynamics to model the observed 21-cm field, our reconstruction proceeds by {combining} the likelihood of a forward simulation to match the observations (under given modeling error and a data noise model) {with the Gaussian prior on initial conditions and maximizing the obtained posterior}. For redshifts z=2 and 4, we are able to reconstruct 21cm field with cross correlation, rc > 0.8 on all scales for both our optimistic and pessimistic assumptions about foreground contamination and for different levels of thermal noise. The performance deteriorates slightly at z=6. The large-scale line-of-sight modes are reconstructed almost perfectly. We demonstrate how our method also provides a technique for density field reconstruction for baryon acoustic oscillations, outperforming standard methods on all scales. We also describe how our reconstructed field can provide superb clustering redshift estimation at high redshifts, where it is otherwise extremely difficult to obtain dense spectroscopic samples, as well as open up a wealth of cross-correlation opportunities with projected fields (e.g. lensing) which are restricted to modes transverse to the line of sight

Adjoint operator approach to shape design for internal incompressible flows

The problem of determining the profile of a channel or duct that provides the maximum static pressure rise is solved. Incompressible, laminar flow governed by the steady state Navier-Stokes equations is assumed. Recent advances in computational resources and algorithms have made it possible to solve the direct problem of determining such a flow through a body of known geometry. It is possible to obtain a set of adjoint equations, the solution to which permits the calculation of the direction and relative magnitude of change in the diffuser profile that leads to a higher pressure rise. The solution to the adjoint problem can be shown to represent an artificially constructed flow. This interpretation provides a means to construct numerical solutions to the adjoint equations that do not compromise the fully viscous nature of the problem. The algorithmic and computational aspects of solving the adjoint equations are addressed. The form of these set of equations is similar but not identical to the Navier-Stokes equations. In particular some issues related to boundary conditions and stability are discussed

Quantacell: Powerful charging of quantum batteries

We study the problem of charging a quantum battery in finite time. We demonstrate an analytical optimal protocol for the case of a single qubit. Extending this analysis to an array of N qubits, we demonstrate that an N-fold advantage in power per qubit can be achieved when global operations are permitted. The exemplary analytic argument for this quantum advantage in the charging power is backed up by numerical analysis using optimal control techniques. It is demonstrated that the quantum advantage for power holds when, with cyclic operation in mind, initial and final states are required to be separable.Comment: 11 pages, 3 figures, comments welcom

Tightening Quantum Speed Limits for Almost All States

Conventional quantum speed limits perform poorly for mixed quantum states: They are generally not tight and often significantly underestimate the fastest possible evolution speed. To remedy this, for unitary driving, we derive two quantum speed limits that outperform the traditional bounds for almost all quantum states. Moreover, our bounds are significantly simpler to compute as well as experimentally more accessible. Our bounds have a clear geometric interpretation; they arise from the evaluation of the angle between generalized Bloch vectors.Comment: Updated and revised version; 5 pages, 2 figures, 1 page appendi

Preterm nutritional intake and MRI phenotype at term age: a prospective observational study

Objective: To describe (1) the relationship between nutrition and the preterm-at-term infant phenotype, (2) phenotypic differences between preterm-at-term infants and healthy term born infants and (3) relationships between somatic and brain MRI outcomes. Design: Prospective observational study. Setting: UK tertiary neonatal unit. Participants: Preterm infants (<32 weeks gestation) (n=22) and healthy term infants (n=39) Main outcome measures: Preterm nutrient intake; total and regional adipose tissue (AT) depot volumes; brain volume and proximal cerebral arterial vessel tortuosity (CAVT) in preterm infants and in term infants. Results: Preterm nutrition was deficient in protein and high in carbohydrate and fat. Preterm nutrition was not related to AT volumes, brain volume or proximal CAVT score; a positive association was noted between human milk intake and proximal CAVT score (r=0.44, p=0.05). In comparison to term infants, preterm infants had increased total adiposity, comparable brain volumes and reduced proximal CAVT scores. There was a significant negative correlation between deep subcutaneous abdominal AT volume and brain volume in preterm infants (r=−0.58, p=0.01). Conclusions: Though there are significant phenotypic differences between preterm infants at term and term infants, preterm macronutrient intake does not appear to be a determinant. Our preliminary data suggest that (1) human milk may exert a beneficial effect on cerebral arterial vessel tortuosity and (2) there is a negative correlation between adiposity and brain volume in preterm infants at term. Further work is warranted to see if our findings can be replicated and to understand the causal mechanisms

Exploring the implications of the influence of organisational culture on work-life balance practices: evidence from Nigerian medical doctors

Purpose - Whilst significant evidence of western work-life balance (WLB) challenges exists, studies that explore Sub-Saharan Africa (SSA) are scarce. This article explores how organisational culture in Nigerian medical organisations influences doctors’ WLB and examines the implications of supportive and unsupportive cultures on doctors’ WLB. Methodology - The paper uses qualitative data gleaned from semi-structured interviews of 60 medical doctors across the six geo-political zones of Nigeria in order to elicit WLB challenges within the context of organisational culture. Findings - The findings show that organisational culture strongly influences employees’ abilities to use WLB policies. Unsupportive culture resulting from a lack of support from managers, supervisors, and colleagues together with long working hours influenced by shift-work patterns, a required physical presence in the workplace, and organisational time expectations exacerbate the challenges that Nigerian medical doctors face in coping with work demands and non-work related responsibilities. Our findings emphasise how ICT and institutions also influence WLB. Originality/value – The paper addresses the under-researched SSA context of WLB and emphasises how human resource management policies and practices are influenced by the complex interaction of organisational, cultural, and institutional settings

Fetomaternal outcome in pregnancy with oligohydramnios: a prospective study

Background: Oligohydramnios is defined as amniotic fluid index 30 weeks.Results: The most common risk factor associated with oligohydramnios was hypertensive disorder of pregnancy (35%) followed by intra uterine growth restriction (31%), preterm rupture of membranes (17%), post-datism (5%) and about 12% were due to idiopathic causes. Among cases majority were primigravida (43%). Lower segment caesarean section was done in 86 cases (43%), and main indication was fetal distress. There was no maternal mortality in the study. NICU admission for low birth weight (26%), pre-maturity (20%), meconium aspiration syndrome (8%), congenital anomalies (8%). Among congenital anomalies, posterior urethral valve had highest incidence (50%) followed by renal agenesis (25%). The neonatal mortality was 5%.Conclusions: Oligohydramnios adversely affects the perinatal outcome. Therefore, it requires meticulous assessment, prompt detection, timely management and treating underlying condition. However, a favourable outcome can be expected by good antenatal and intrapartum surveillance and neonatal care