Carbapenem-resistant
(CRE) represent a health threat, but effective control interventions remain unclear. Hospital wastewater sites are increasingly being highlighted as important potential ...reservoirs. We investigated a large
carbapenemase (KPC)-producing
outbreak and wider CRE incidence trends in the Central Manchester University Hospital NHS Foundation Trust (CMFT) (United Kingdom) over 8 years, to determine the impact of infection prevention and control measures. Bacteriology and patient administration data (2009 to 2017) were linked, and a subset of CMFT or regional hospital KPC-producing
isolates (
= 268) were sequenced. Control interventions followed international guidelines and included cohorting, rectal screening (
= 184,539 screens), environmental sampling, enhanced cleaning, and ward closure and plumbing replacement. Segmented regression of time trends for CRE detections was used to evaluate the impact of interventions on CRE incidence. Genomic analysis (
= 268 isolates) identified the spread of a KPC-producing
outbreak clone (strain A, sequence type 216 ST216;
= 125) among patients and in the environment, particularly on 2 cardiac wards (wards 3 and 4), despite control measures. ST216 strain A had caused an antecedent outbreak and shared its KPC plasmids with other
lineages and
species. CRE acquisition incidence declined after closure of wards 3 and 4 and plumbing replacement, suggesting an environmental contribution. However, ward 3/ward 4 wastewater sites were rapidly recolonized with CRE and patient CRE acquisitions recurred, albeit at lower rates. Patient relocation and plumbing replacement were associated with control of a clonal KPC-producing
outbreak; however, environmental contamination with CRE and patient CRE acquisitions recurred rapidly following this intervention. The large numbers of cases and the persistence of
in
, including pathogenic lineages, are of concern.
Cobalt doped magnetite nanoparticles (Co
x
Fe
3−
x
O
4
NPs) are investigated extensively because of their potential hyperthermia application. However, the complex interrelation among chemical ...compositions and particle size means their correlation with the magnetic and heating properties is not trivial to predict. Here, we prepared Co
x
Fe
3−
x
O
4
NPs (0 ≤
x
≤ 1) to investigate the effects of cobalt content and particle size on their magnetic and heating properties. A detailed analysis of the structural features indicated the similarity between the crystallite and particle sizes as well as their non-monotonic change with the increase of Co content. Magnetic measurements for the Co
x
Fe
3−
x
O
4
NPs (0 ≤
x
≤ 1) showed that the blocking temperature, the saturation magnetization, the coercivity, and the anisotropy constant followed a similar trend with a maximum at
x
= 0.7. Moreover,
57
Fe Mössbauer spectroscopy adequately explained the magnetic behaviour, the anisotropy constant, and saturation magnetization of low Co content samples. Finally, our study shows that the relaxation loss is a primary contributor to the SAR in Co
x
Fe
3−
x
O
4
NPs with low Co contents as well as their potential application in magnetic hyperthermia.
The interrelation among chemical compositions, structure, and heating properties of cobalt doped magnetite nanoparticles (Co
x
Fe
3−
x
O
4
NPs) for their potential hyperthermia application.
•Review of AM Ti–6Al–4V fatigue performance.•Effect of surface treatment on AM fatigue performance.•Effect of heat treatment on AM fatigue performance.
To realize the potential benefits of additive ...manufacturing technology in airframe and ground vehicle applications, the fatigue performance of load bearing additively manufactured materials must be understood. Due to the novelty of this rapidly developing technology, a very limited, yet swiftly evolving literature exists on the topic. Motivated by these two points, we have attempted to catalog and analyze the published fatigue performance data of an additively manufactured alloy of significant technological interest, Ti–6Al–4V. Focusing on uniaxial fatigue performance, we compare to traditionally manufactured Ti–6Al–4V, discussing failure mechanisms, defects, microstructure, and processing parameters. We then attempt to identify key knowledge gaps that must be addressed before AM technology can safely and effectively be employed in critical load bearing applications.
•Fatigue performance of powder bed fusion additive manufactured Ti-6Al-4V.•Effects of AM fabrication and post fabrication processes on fatigue performance.•Life predictions based on effective defect ...size from extreme value statistics.•Analysis and predictions of a link component as an illustrative application example.
Part I of these two-part paper series focused on the process and structure relationships, effect of powder feedstock, fabrication parameters, and post fabrication treatments on the resulting microstructure, defect characteristics, and surface quality of the fabricated Ti-6Al-4V parts. This second part extends the study by evaluating the effect of the aforementioned factors on axial, torsion, and multiaxial fatigue behavior of the additively manufactured (AM) Ti-6Al-4V specimens. Despite the advantages of additive manufacturing techniques discussed in Part I, they are still rarely used in fatigue critical load carrying applications, partly due to insufficient understanding of fatigue behavior and its dependence on variations in material microstructure and defects. This becomes even more challenging when other process characteristics of AM including build orientation, residual stresses, and surface roughness are considered. This paper discusses these effects, as well as machine-to-machine variability and the effects of specimen geometry and size, post heat treatment, and multiaxial stress state. Experimental uniaxial, torsion, and multiaxial fatigue test results recently generated by the authors for laser beam powder bed fusion- produced Ti-6Al-4V alloy are reviewed. The observed behaviors and the influence of the aforementioned effects are then related to the resulting microstructure and defect characteristics discussed in Part I. Fatigue life prediction results for specimens based on the effective defect size calculated by extreme value statistics (EVS) of the internal defects and surface roughness are also presented and compared with experimental data. The observed behaviors and specimen test results are then used for fatigue life analysis and predictions of a link component as an illustrative application example.
•High/low energy input during AM favors spherical pores/lack-of-fusion, respectively.•Lack-of-fusion defects are more detrimental to fatigue performance.•Post AM hot isostatic pressing cannot fully ...eliminate defects due to entrapped gas.•Reused powder can lead to reduced defect content and improved fatigue life.•Prior-beta morphology can be altered by tuning AM process and/or heat treatments.
Additive manufacturing provides an appealing means to process titanium alloy parts with new levels of conformability, complexity, and weight reduction. However, due to the heating/cooling rates and heat transfer associated with directed energy source material processing, the as-built AM parts contain unique material and microstructural features. In order to confidently manufacture fatigue critical additive manufactured (AM) Ti-6Al-4V parts, a better understanding of the interrelationships between powder feedstock, AM processes, structure of the processed parts, their resulting mechanical properties, and their performance under realistic loadings is necessary. Part I of this two-part collection focuses on the powder-process-structure relationships and how powder feedstock, manufacturing, and post-processing conditions can affect the microstructure and defect features that ultimately contribute to the fatigue performance of Ti-6Al-4V parts. The material and physical phenomena inherent to the AM process of Ti-6Al-4V are discussed in detail and related to the phase composition/structure, grain morphology, surface characteristics, defect size/distribution, and post-process treatments available for AM parts. This investigation is the foundation for the structure-performance relationships that will be discussed in detail in Part II.
Optimization problems of beamforming in multi-user amplify-and-forward (AF) wireless relay networks are indefinite (nonconvex) quadratic programs, which require effective computational solutions. ...Solutions to these problems have often been obtained by relaxing the original problems to semi-definite programs (SDPs) of convex optimization. Most existing works have claimed that these relaxed SDPs actually provide the optimal beamforming solutions. This paper, however, shows that this is not the case in many practical scenarios where SDPs fail to provide even a feasible beamforming solution. To fill this gap, we develop in this paper a nonsmooth optimization algorithm, which provides the optimal solution at low computational complexity.
It has been known that a La2/3Ca1/3MnO3 (LMO) bulk sample has the maximum magnetic entropy change (|ΔSmax|) larger than |ΔSmax| of Gd – a conventional magnetocaloric (MC) material. However, such ...large change just takes place in a narrow range of temperature because of its first-order character. This influences the working temperature range (ΔT) and relative cooling power (RCP) of LMO. Previous works have revealed that the fabrication of LMO nanoparticles with the second-order character would improve the magnitude of ΔT and RCP, and reduce magnetic hysteresis losses. In this work, we suggest that the combination of LMO nanoparticles (NPs) with Gd powder as nanocomposites (NCPs), termed (100-x)LMO + xGd with x = 50 and 75 wt%, further enhances ΔT from 60 to ∼94 K (in the range T = 220–314 K) for applied fields H = 5–20 kOe. These values are larger than those of initial materials Gd and LMO NPs (ΔT ≈ 40 K), reported composites (ΔT < 50 K), and even the composites fabricated from a LMO bulk and Gd powder (ΔT < 60 K) in the same fields. Additionally, all NCPs exhibit the second-order character, and RCP of optimal NCPs is nearly comparable to that of Gd. These features demonstrate application potentials of NCPs for conventional refrigerators operating in a large temperature range.
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•Magnetic and magnetocaloric behaviors of La2/3Ca1/3MnO3/Gd nanocomposites.•Increased magnetocaloric response in a large temperature range.•Working temperature range enhances remarkably from 60 to ∼90 K.•Relative cooling power of optimal composites is comparable to that of Gd.
•Analysis of literature data provides insight into the mechanisms by which HIP improves fatigue life.•HIP improves fatigue life of PBF Ti-6Al-4V by decreasing the fraction of the defect population ...that can initiate fatigue cracks and by changing the microstructure surrounding defects.•The idea that microstructure near defects evolves differently than the microstructure away from defects during HIP treatment is supported by EBSD orientation maps.•The gained understanding provides initial guidance on HIP soak parameters (Temperature-Pressure-Time) to improve high cycle fatigue performance in PBF Ti-6Al-4V.
Hot isostatic pressing (HIP) is often needed to obtain powder bed fused (PBF) Ti-6Al-4V parts with good fatigue performance. This manuscript attempts to clarify the mechanisms through which HIP treatment acts to improve high cycle fatigue performance. Several mechanisms are considered and examined against experimental data sets available in the literature. The results suggest that HIP may act most significantly by decreasing the fraction of the defect population that can initiate fatigue cracks, both by decreasing defect sizes below a threshold and by changing the microstructure that surrounds defects. Given the novelty of the latter conclusion, an electron backscatter diffraction microscopy study was performed for validation. The gained understanding provides initial guidance on the choice of optimum HIP soak parameters (Temperature-Pressure-Time) for the high cycle fatigue performance of PBF Ti-6Al-4V.
The mechanical performance of powder bed fused (PBF) components can vary significantly, even within a single build with processing parameters kept constant. To better understanding this variability, ...two sets of uniaxial fatigue specimens were examined, differing only in gage section surface area and location on the build plate. Significantly different fatigue performance was observed between the two geometries, despite being manufactured in the same laser power bed fusion (L-PBF) build. Possible explanations for the difference in fatigue performance were then examined, such as mechanical interactions between fatigue cracks and the specimen geometry, microstructure, surface roughness, increased surface area, and build defects. Differences in the density of near surface build defects were identified as the cause of the difference in fatigue performance between the two sets of specimens. The difference in fatigue performance was found to be predictable from a simple weakest link model given knowledge of the ratio of defect densities. Subsequently, an attempt was made to predict the difference in defect densities using a full resolution thermal model. The model results suggest additional details such as the nonuniformity in powder spreading, laser-plume interactions, and/or the interference of debris from previously scanned tracks may be necessary ingredients for process-structure-performance predictions of fatigue critical PBF components.
•Direct and indirect measurements magnetocaloric effect in Pr0.7Sr0.2Ca0.1MnO3.•Specific heat, thermal diffusivity, thermal conductivity, resistivity Pr0.7Sr0.2Ca0.1MnO3.•Correlation of the MCE and ...thermophysical properties near the FM-PM phase transition.•The giant value of the RCP ~814 J/kg for the Pr0.7Sr0.2Ca0.1MnO3 sample at H = 80 kOe.
We present the results of a comparative analysis of the magnetocaloric effect (MCE) in Pr0.7Sr0.2Ca0.1MnO3, through direct and indirect measurements, using experimentally measured magnetization, specific heat, magnetostriction, resistivity, thermal diffusivity and thermal conductivity parameters. We have demonstrated that the change in each parameter in response to a magnetic field near the ferromagnetic-paramagnetic phase transition temperature of the material correlates with the change in magnetic entropy. These findings allow us to interrelate these parameters and provide an alternative, effective approach for accessing the usefulness of magnetocaloric materials.
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