Photographic study of high-flux subcooled flow boiling and critical heat flux

This study examines both high-flux flow boiling and critical heat flux (CHF) under highly subcooled conditions using FC-72 as working fluid. Experiments were performed in a horizontal flow channel that was heated along its bottom wall. High-speed video imaging and photomicrographic techniques were used to capture interfacial features and reveal the sequence of events leading to CHF. At about 80% of CHF, bubbles coalesced into oblong vapor patches while sliding along the heated wall. These patches grew in size with increasing heat flux, eventually evolving into a fairly continuous vapor layer that permitted liquid contact with the wall only in the wave troughs between vapor patches. CHF was triggered when this liquid contact was finally halted. These findings prove that the CHF mechanism for subcooled flow boiling is consistent with the interfacial lift-off mechanism proposed previously for saturated flow boiling.     

Exploring isolated lignin material from oil palm biomass waste in green composites

Lignin obtained from oil palm biomass empty fruit bunches (EFB) fibers, has been used as curing agent in green epoxy composites. Epoxy–lignin composites, with varying lignin content (15%, 20%, 25% and 30%), reinforced with EFB fiber were prepared. The effect of EFB-based lignin on the mechanical, thermal and morphology properties of the composites were investigated and compared with the composites cured with isophorone diamine curing agent. The improved thermal stability and the observed microstructure of the fractured surface of the composites were attributed to good fiber–matrix interaction, induced by the curing agent. The epoxy composites cured with 25% lignin content proved to be a better matrix and gave optimum value compared with other formulations which was confirmed by its mechanical, thermal and morphological properties.     

Nf1 regulates hematopoietic progenitor cell growth and ras signaling in response to multiple cytokines

Neurofibromin, the protein encoded by the NF1 tumor-suppressor gene, negatively regulates the output of p21(ras) (Ras) proteins by accelerating the hydrolysis of active Ras-guanosine triphosphate to inactive Ras-guanosine diphosphate. Children with neurofibromatosis type 1 (NF1) are predisposed to juvenile chronic myelogenous leukemia (JCML) and other malignant myeloid disorders, and heterozygous Nf1 knockout mice spontaneously develop a myeloid disorder that resembles JCML. Both human and murine leukemias show loss of the normal allele. JCML cells and Nf1-/- hematopoietic cells isolated from fetal livers selectively form abnormally high numbers of colonies derived from granulocyte-macrophage progenitors in cultures supplemented with low concentrations of granulocyte-macrophage colony stimulating factor (GM-CSF). Taken together, these data suggest that neurofibromin is required to downregulate Ras activation in myeloid cells exposed to GM-CSF. We have investigated the growth and proliferation of purified populations of hematopoietic progenitor cells isolated from Nf1 knockout mice in response to the cytokines interleukin (IL)-3 and stem cell factor (SCF), as well as to GM-CSF. We found abnormal proliferation of both immature and lineage-restricted progenitor populations, and we observed increased synergy between SCF and either IL-3 or GM-CSF in Nf1-/- progenitors. Nf1-/- fetal livers also showed an absolute increase in the numbers of immature progenitors. We further demonstrate constitutive activation of the Ras-Raf-MAP (mitogen-activated protein) kinase signaling pathway in primary c-kit+ Nf1-/- progenitors and hyperactivation of MAP kinase after growth factor stimulation. The results of these experiments in primary hematopoietic cells implicate Nf1 as playing a central role in regulating the proliferation and survival of primitive and lineage-restricted myeloid progenitors in response to multiple cytokines by modulating Ras output.     

Thermal Stresses in Spherical Shells

This paper presents an iterative finite-difference technique for the analysis of axisymmetric spherical shells with variable wall thickness. The formulation is based on thin elastic shell theory. One-dimensional finite-difference points are used to discretize the shell into strips along the meridian, and an iterative technique is employed to determine the normal and meridional displacements. The stress resultants and bending stresses are then evaluated. Unlike existing analytical and finite-difference techniques, the proposed method is applicable with ease to any variation in rigidity along the meridian, to general loading conditions, and to steep and shallow shells. Results are presented and compared with those of the finite-element method.     

Linear Programming Approach to Optimize Strategic Investment in the Construction Workforce

The construction industry in the United States and other parts of the world has been facing several challenges, including a shortage of skilled workers. A review of the relevant body of knowledge indicates that one of the key reasons for this problem is the absence of human resource management strategies for construction workers at project, corporate, regional, or industry levels. This paper addresses the issues of workforce training and allocation on construction projects. It presents a framework to optimize the investment in, and to make the best use of, the available workforce with the intent to reduce project costs and improve schedule performance. A linear program model, entitled the Optimal Workforce Investment Model, is built to provide an optimization-based framework for matching supply and demand of construction labor most efficiently through training, recruitment, and allocation. Given a project schedule or demand profile and the available pool of workers, the suggested model provides human resource managers a combined strategy for training the available workers and hiring additional workers. The input data to the proposed model consists of a certain available labor pool, cost figures for training workers in different skills, the cost of hiring workers, hourly labor wages, and estimates of affinities between the different considered skills. The objective of the model is to minimize labor costs while satisfying project labor demands. Results from application of the model to typical situations are presented, and recommendations for future developments are made.     

Assessment of proliferative and colony-forming capacity after successive in vitro divisions of single human CD34+ cells initially isolated in G0

Exit of primitive hematopoietic progenitor cells (HPCs) from the G0 phase of the cell cycle in response to in vitro cytokine stimulation is a limiting step in successful ex vivo expansion. Simultaneous DNA/RNA staining with Hoechst 33342 and pyronin Y was used to separate human bone marrow CD34+ cells residing in G0 (G0CD34+) from those cycling in G1 and S/G2+M. Compared with CD34+ cells isolated in G1, G0CD34+ cells were characterized by a delayed response to cytokine stimulation and were enriched for long-term hematopoietic culture-initiating cells. We next compared the activation kinetics of individually sorted G0CD34+ cells stimulated with stem cell factor (SCF), flt3-ligand (FL), or interleukin-3 (IL-3) as single factors. In a novel clonal proliferation assay, the functional status of cells that had remained quiescent after an initial 7-day period and of those that had completed successive division cycles under each of these three factors was evaluated by assessment of subsequent proliferative capacity and maintenance of colony-forming cell precursor (pre-CFC) activity. All three cytokines were equally able to support the survival of primitive HPCs in the absence of cell division. Cells that did not respond to any cytokine stimulation for 7 days retained higher proliferative and pre-CFC activities than dividing cells. The hematopoietic function of cells that divided in response to SCF, FL, or IL-3 decreased after each division cycle. However, G0CD34+ cells displayed a heterogeneous response pattern to cytokine stimulation whereby SCF appeared to have a superior ability to promote the cycling of cells with high proliferative and pre-CFC activities. These results indicate that HPCs reside in opposing hierarchies of hematopoietic potential and responsiveness to cytokine stimulation. The data also begin to indicate relationships between cellular division in response to different stimuli and maintenance of hematopoietic function.     

Radiation-Induced Charge Transport and Charge Buildup in SiO2 Films at Low Temperatures

Studies of the temporal, temperature, and electricfield dependences of radiation-induced charge transport have been performed for radiation-hardened SiO2 films. At room temperature for high applied fields, nearly all electrons and holes generated in the oxide by a pulse of ionizing radiation (5-keV electrons) drift to the interfaces, whereas at low temperatures only electrons contribute to observed transport for relatively low fields. Below ~130°K at high fields, field-induced emission of trapped holes occurs, giving rise to collection within seconds of a significant fraction of the total number of holes generated. The present hole transport data are accounted for quite well in terms of a multiple-trapping model with a spread in trap levels ranging from ~0.3 to ~0.5 eV from the valence band. Comparison with the stochastic hopping transport model is made and that model is found to be less satisfactory in explaining these data. Charge buildup was examined in a Co60 environment and it is demonstrated that oxides exhibiting radiation tolerance at room temperature display severe radiation-induced changes at 77°K. It is also demonstrated that low-temperature charge buildup problems can be alleviated either by employing an ion-implanted oxide or by applying a relatively high field to the oxide during irradiation.     

One-Dimensional Model for Multi-Barge Flotillas Impacting Bridge Piers

Abstract:   The serious consequence of barge-bridge collisions necessitates the study of barge impact loadings on bridges. This article introduces an elastoplastic spring-mass model for the analysis of multi-barge flotillas colliding with bridge piers at zero angle of attack. The model accounts for the essential factors pertaining to barge/flotilla impacts, such as pier geometry and stiffness, and dynamic interaction between barges. A method to identify the elastoplastic behavior of barge crushing is also presented. The proposed method generates impact force time-histories for a multitude of flotilla configurations in a matter of minutes, which is especially valuable in probabilistic analysis requiring many collision simulations. The results from this study are compatible with the respective impact time-histories produced by exhaustive finite element simulations. A bridge pier impacted by a three-barge and a 15-barge flotilla is studied.     

Sonocrystallisation of sodium chloride particles for inhalation

Fine sodium chloride particles are of pharmaceutical interest in aerosol delivery for diagnosis of asthma and bronchial related disorders. In this paper, stable NaCl particles with size ranging from approximately to sub-micron range were achieved by sonocrystallisation. The effects of sonocrystallisation temperature, ultrasonic power output and salt concentration were investigated in the ranges of , 22-60 W and 8-34 g/100 g water, respectively, under a fixed ultrasonic frequency of 20 kHz. Size and morphology characterisation of particles were undertaken using laser diffraction and scanning electron microscopy. Optimally prepared particles were spray dried followed by in vitro impaction test for inhalation efficiency determination using an Aeroliser^®. Optimal conditions of temperature ), ultrasonic power output and salt concentration water) exist that reduced the size of the crystals to the sub-micron scale. Spray drying increased the size of the prepared particles and altered the cubic shape to more rounded morphology. The fine particle fraction (based on recovery) was improved from approximately 12 to 34% when dispersion air flow rate was increased from 60 to 120 L/min. Sonocrystallisation represents an effective method for the preparation of NaCl particles suitable for pharmaceutical inhalation. The main advantage of this method is that it is rapid, simple and produces small crystal NaCl particles suitable for inhalation.