DEVELOPMENT OF A DICHOTOMOUS SLIT NOZZLE VIRTUAL IMPACTOR

A high-volume slit nozzle virtual impactor has been developed to collect fine and coarse particles. The size cut-off and particle loss characteristics of the developed slit virtual impactor agree well with those of the 16.7 lmin⁻¹ commercially available dichotomous sampler. The effects of various flow and physical design parameters on the collection of both fine and coarse particles have been investigated. The results of these tests indicated that many of the theoretical principles established for round nozzle virtual impactors can be successfully applied to slit nozzle virtual impactors. However, the effects of the flow volume and Reynolds number (Re) on the cut-off behavior and particle losses are more pronounced for slit virtual impactors. The impactor's particle size cutpoint decreased as the total inlet flow and Re increased. For Re<about 7000, particle losses increased with particle size. For Re of about 7000, particle losses exhibited a maximum near the 50% cutpoint, which is typical in round nozzle virtual impactors. For Re>7000, losses of fine particles were significant, while coarse particle losses were low. Changes in the minor-to-total flow ratio and collection slit width also affected particle losses.     

Shape optimization for drag reduction in linked bodies using evolution strategies

We present results from the shape optimization of linked bodies for drag reduction in simulations of incompressible flow at moderate Reynolds numbers. The optimization relies on the covariance matrix adaptation evolution strategy (CMA-ES) and the flow simulations use vortex methods with the Brinkman penalization to enforce boundary conditions in complex bodies. We exploit the inherent parallelism of CMA-ES, by implementing a multi-host framework which allows for the distribution of the expensive cost function evaluations across parallel architectures, without being limited to one computing facility. This study repeats in silico for the first time Ingo Rechenberg’s pioneering wind tunnel experiments for drag reduction that led to the inception of evolution strategies. The simulations confirm that the results of these experimental studies indicate a flat plate is not the optimal solution for drag reduction in linked bodies. We present the vorticity field of the flow and identify the governing mechanisms for this drag reduction by the slightly corrugated linked plate configuration.     

Localizable entanglement in antiferromagnetic and mixed Heisenberg chains: a quantum Monte Carlo study

We investigate entanglement formation in antiferromagnetic and mixed anisotropic, finite, one-dimensional Heisenberg chains with and without the presence of a uniform magnetic field. We explore the thermal entanglement created in terms of the bounds of the localizable entanglement and the possibility for quantum phase transitions in the zero field cases by means of standard quantum Monte Carlo method.     

Diffusion-weighted echo planar MR imaging of the neck at 3 T using integrated shimming: comparison of MR sequence techniques for reducing artifacts caused by magnetic-field inhomogeneities

Objective

Our objective was to compare available techniques reducing artifacts in echo planar imaging (EPI)-based diffusion-weighed magnetic resonance imaging MRI (DWI) of the neck at 3 Tesla caused by B0-field inhomogeneities.

Materials and methods

A cylindrical fat–water phantom was equipped with a Maxwell coil allowing for additional linear B0-field variations in z-direction. The effect of increasing strength of this superimposed gradient on image quality was observed using a standard single-shot EPI-based DWI sequence (sEPI), a zoomed single-shot EPI sequence (zEPI), a readout-segmented EPI sequence (rsEPI), and an sEPI sequence with integrated dynamic shimming (intEPI) on a 3-Tesla system. Additionally, ten volunteers were examined over the neck region using these techniques. Image quality was assessed by two radiologists. Scan durations were recorded.

Results

With increasing strength of the external gradient, marked distortions, signal loss, and failure of fat suppression were observed using sEPI, zEPI, and rsEPI. These artifacts were markedly reduced using intEPI. Significantly better in vivo image quality was also observed using intEPI compared with the other techniques. Scan time of intEPI was similar to sEPI and zEPI and shorter than rsEPI.

Conclusion

The use of integrated 2D shim and frequency adjustment for EPI-based DWI results in a significant improvement in image quality of the head/neck region at 3 Tesla. Combining integrated shimming with rsEPI or zEPI can be expected to provide additional improvements.

     

Comparison of T1-weighted 2D TSE, 3D SPGR,and two-point 3D Dixon MRI for automated segmentation of visceral adipose tissue at 3 Tesla

Objectives

To evaluate and compare conventional T1-weighted 2D turbo spin echo (TSE), T1-weighted 3D volumetric interpolated breath-hold examination (VIBE), and two-point 3D Dixon-VIBE sequences for automatic segmentation of visceral adipose tissue (VAT) volume at 3 Tesla by measuring and compensating for errors arising from intensity nonuniformity (INU) and partial volume effects (PVE).

Materials and methods

The body trunks of 28 volunteers with body mass index values ranging from 18 to 41.2 kg/m² (30.02 ± 6.63 kg/m²) were scanned at 3 Tesla using three imaging techniques. Automatic methods were applied to reduce INU and PVE and to segment VAT. The automatically segmented VAT volumes obtained from all acquisitions were then statistically and objectively evaluated against the manually segmented (reference) VAT volumes.

Results

Comparing the reference volumes with the VAT volumes automatically segmented over the uncorrected images showed that INU led to an average relative volume difference of ?59.22 ± 11.59, 2.21 ± 47.04, and ?43.05 ± 5.01 % for the TSE, VIBE, and Dixon images, respectively, while PVE led to average differences of ?34.85 ± 19.85, ?15.13 ± 11.04, and ?33.79 ± 20.38 %. After signal correction, differences of ?2.72 ± 6.60, 34.02 ± 36.99, and ?2.23 ± 7.58 % were obtained between the reference and the automatically segmented volumes. A paired-sample two-tailed t test revealed no significant difference between the reference and automatically segmented VAT volumes of the corrected TSE (p = 0.614) and Dixon (p = 0.969) images, but showed a significant VAT overestimation using the corrected VIBE images.

Conclusion

Under similar imaging conditions and spatial resolution, automatically segmented VAT volumes obtained from the corrected TSE and Dixon images agreed with each other and with the reference volumes. These results demonstrate the efficacy of the signal correction methods and the similar accuracy of TSE and Dixon imaging for automatic volumetry of VAT at 3 Tesla.

     

Investigation of biofilm growth and attrition in a three‐phase airlift bioreactor using 35SO42− as a radiolabelled tracer

The growth and biomass loss pattern for immobilized cells growing on diatomaceous earth particles in a three‐phase airlift bioreactor (TPALB) is studied using ³⁵S as a radiolabelled tracer. A monoculture of Beneckea natriegens was grown immobilized on support particles in a 3 L TPALB. Sterile conditions were maintained during the experiments, and n‐propanol was used as the sole carbon source. After the system reached steady state, the unlabelled sulfate (SO₄^2?) in the feed tank was substituted by a radioactive grade (³⁵SO₄^2?), and the assimilation of ³⁵S in the immobilized and in the suspended cells was monitored. The results indicated that the growth rate of immobilized biomass was not uniform throughout the biofilm. More specifically, it was concluded that cells growing closer to the external biofilm layer exhibit a higher growth rate, and that biomass loss from the biofilm was through attrition at the outer biofilm surface rather than by sloughing off of whole sections of biofilm. Copyright © 2006 Society of Chemical Industry     

On performance of slowly varying systems

In this paper we present a result on the performance of slowly time varying systems. In particular we show that the performance of such systems cannot be much worse than that of the frozen-time systems which are time invariant. We also demonstrate via an example that optimal frozen-time design may in general result to far from optimal performance even though the time variations of the system can be arbitrarily slow.     

The addition of paclitaxel to continuous infusion 5-fluorouracil is an active regimen for metastatic breast cancer

We investigated tissue staining for Bcl-2 and Bax proteins, which regulate apoptosis, as indicators of chemotherapeutic effect in patients with gastric cancer. In 23 patients with gastric carcinoma biopsy specimens were obtained endoscopically prior to chemotherapy and stained immunohistochemically with anti-Bcl-2 and anti-Bax antibodies. Patients then were treated with continuous infusion of 5-FU and cisplatin. No correlation was seen between chemotherapeutic effect and Bcl-2 or Bax alone. However, among the Bax-positive cases, the patients with Bcl-2-positive tumors were significantly more chemoresistant (p = 0.036) and had worse prognoses (p = 0.008) than Bcl-2-negative cases. Therefore, immunohistochemical staining for Bcl-2 protein may predict chemotherapeutic efficacy or guide specific therapeutic choices in treating Bax-positive tumors.     

Numerical stability and convergence criteria for equations for dynamic fracture in DCB composite specimens

The stability and convergence criteria for numerical solutions of the governing equations for dynamic crack propagation in DCB unidirectional composite specimens are determined. The stability criteria are given explicitly and it is concluded that the convergence requirements will be met automatically by solutions which satisfy the stability criteria.     

Effect of high-pressure treatment at various temperatures on indigenous proteolytic enzymes and whey protein denaturation in bovine milk

The objective of the present study was to determine the effect of high pressure (HP) processing (200, 450 and 650 MPa) at various temperatures (20, 40 and 55 degrees C) on the total plasmin plus plasminogen-derived activity (PL), plasminogen activator(s) (PA) and cathepsin D activities and on denaturation of major whey proteins in bovine milk. Data indicated that transfer of both PL and PA from the casein micelles to milk serum occurred at all pressures utilized at room temperature (20 degrees C). In addition to the transfer of PL and PA from micelles, there were reductions in activities of PL (16-18%) and PA (38-62%) for the pressures 450 and 650 MPa, at room temperature. There were synergistic negative effects between pressure and temperature on residual PL activity at 450 and 650 MPa and on residual PA activity only at 450 MPa. Cathepsin D activity in the acid whey from HP-treated milk was in general baroresistant at room temperature. The residual activity of cathepsin D decreased significantly at 650 MPa and 40 degrees C and at the pressures 450 and 650 MPa at 55 degrees C. Synergistic negative effects on the amount of native beta-lactoglobulin were observed at 450 and 650 MPa and on the amount of native alpha-lactalbumin at 650 MPa. There were significant correlations between enzymatic activities (PL, PA and cathepsin D) and the residual native beta-lactoglobulin and alpha-lactalbumin in bovine milk. In conclusion, HP significantly affected the activity of indigenous proteolytic enzymes and whey protein denaturation in bovine milk. Reduction in activity of indigenous enzymes (PL, PA and cathepsin D) and transfer of PL and PA from the casein to milk serum induced by HP is expected to have a profound effect on cheese yield, proteolysis during cheese ripening and quality of UHT milk during storage.