Collapse Recovery Research Articles

Study of the collapse and recovery of Eucalyptus urophydis during conventional kiln drying

The collapse of Eucalyptus urophydis wood during conventional kiln drying prevents the widespread use of its wood products. This research aims to explore its collapse and recovery characteristics, as well as the effect of continuous and cyclic drying. The collapse was measured by total shrinkage, and cell deformation was observed at three critical points using scanning electron microscopy. The collapse and recovery were investigated by integrating the shrinkage curves and observing the cell micro-deformation. The results showed that the continuous drying rate was faster than that of cyclic drying, especially when the moisture content was below the fiber saturation point. Compared with relative humidity, the temperature had a greater effect on the tangential absolute dry shrinkage. Although cyclic drying decreased collapse, its effect was apparent only at low temperatures and was weak at high temperatures. The collapse recovery time was affected by temperature, and recovery occurred quickly at high temperatures, and the moisture content range was longer. In contrast to continuous drying, the high relative humidity period during cyclic drying led to earlier collapse recovery. The degree and trends of microscopic collapse were consistent with the macroscopic scanning measurements.

Engineering a Unified Dielectric Solution for AlGaN/GaN MOS-HFET Gate and Access Regions

Typically GaN metal-oxide-semiconductor heterojunction-field-effect transistors (MOS-HFETs) have used two separate dielectrics for the gate and access regions. However, as this article shows, with proper gate-stack engineering, a unified dielectric solution can be achieved for the transistor. HfO2 dielectrics were deposited by atomic layer deposition (ALD). Two types of oxidants were investigated, namely, water (H2O) and ozone (O3). It was found that MOS-HFETs with O3 oxidant yielded lower threshold voltage ( ${V}_{\text {TH}}$ ) shifts, higher maximum drain current ( ${I}_{\text {DS,max}}$ ) of 340 mA/mm, 20% lower ON-resistance ( ${R}_{ {\mathrm {\scriptscriptstyle {ON}}}}$ ), higher peak transconductance at 112.66 mS/mm, lower hysteresis, and lower gate leakage ( ${5.4} \times {10}^{-{6}}$ A/cm2) compared to water oxidant based MOS-HFETs with ${I}_{\text {DS},\text {max}}$ of 240 mA/mm, 81.38 mS/mm peak transconductance, and ${1.7} \times {10}^{-{4}}$ A/cm2 gate leakage. DC/RF dispersion tests showed MOS-HFETs with O3 oxidant had ~200 $\times $ better current collapse recovery. Temperature characterization and reliability test results, such as high-temperature reverse bias (HTRB), are published for the first time on ALD-HfO2/AlGaN/GaN MOS-HFETs using tetrakis(dimethylamino)hafnium (TDMAH) and O3 precursor. Using an ozone oxidant provided more stability (i.e., less variability in ${R}_{ {\mathrm {\scriptscriptstyle {ON}}}}$ and ${V}_{\text {TH}}$ ) as a function of temperature. Finally, when devices were electrically stressed in the OFF-state, the HTRB test showed minimal ${V}_{\text {TH}}$ drift ( ${V}_{\text {TH}}$ drift (2.5 V) in the case of H2O oxidant.

Collapse and physical properties of native and pre-steamed Eucalyptus camaldulensis and Eucalyptus saligna wood from Tunisia

Eucalyptus is the second major wood species used for Tunisian reforestation since 1957, and they are found around the country in several arboretums. Eucalyptus may be an interesting raw material to the Tunisian wood industry. The main obstacle to its industrial exploitation is its natural propensity to incur internal checking, collapse and a high transverse shrinkage during industrial drying process. This study focused on the physical and mechanical properties of reforested Eucalytus saligna and Eucalyptus camaldulensis from the north west of Tunisia. Moisture content, densities, shrinkages and mechanical properties were determined. Then, the impact of pre-steaming on the physical properties of modified wood was investigated. The results showed that both Eucalyptus possess low dimensional stability and mechanical properties compared to other Eucalyptusspecies from Tunisia, Morocco, Australia and Brazil. These wood characteristics were mainly due to their low density and sensitivity to collapse reactions, occurred during drying. Pre-steaming process reduced Eucalyptswood moisture content, changing the wood permeability and resulting in a residual collapse recovery and a decrease in wood shrinkage. Pre-steaming treated E. camaldulensis and E. saligna wood could be valuable as furniture and/or structural material without being submitted to moisture content variation.

The effects of different inspired oxygen concentration on the pulmonary collapse and postoperative recovery of thoracoscopic surgery

Objective To investigate the effect of different inhalation oxygen concentration on the lung collapse and postoperative recovery of thoracoscopic surgery. Methods Patients who underwent elective thoracoscopic radical resection of lung cancer were randomly divided into group A (n=29) and group B (n=30). Patents in the group A received a gas mixture of oxygen and air (FiO2=50%) whereas and patients in the group B received 100% oxygen(FiO2=100%) until the start of one lung ventilation (OLV). Then, the dependent lungs were ventilated with 50% oxygen during OLV in both groups. The surgeon evaluated the lung collapse using LCS score and Campos score for lung collapse. They were scaled at 1 min after the opening of the pleura(T0), 10 min after the start of OLV (T1), 20 min after the start of OLV (T2) and 30 min after the start of OLV (T3). During two lungs ventilation, arterial blood gases were measured before anesthesia induction, at 10, 20, 30 min after initiation of OLV. The incidence of postoperative atelectasis by chest CT at the third day after operation, hospital length of stay(LOS) and the incidence of patchy consolidation were recorded. Results At T1 and T2, the LCS scores and Campos scales of group B were higher than scores of group A (P 0.05). The oxygen partial pressure of group B was higher than that of the group A before 20 min of OLV, but the difference were not significant after 20 min. The incidence of postoperative atelectasis, LOS and the incidence of patchy consolidation were not different (P>0.05) Conclusions The inhalation of 100% oxygen before the OLV can make the pulmonary collapse effect better, and it has no effect on postoperative recovery. Key words: Video assisted thoracic operation; Pulmonary collapse; Fraction of inspired oxygen; One lung ventilation

A Review of Eucalyptus Wood Collapse and its Control during Drying

The relevant literature is reviewed concerning eucalyptus wood collapse, with a focus on lumber drying technology. Potential future research is summarized regarding where potential future work may focus. Eucalyptus is often limited as a solid wood products material due to microstructural collapse and interior cracking that may occur during drying. To prevent the drying collapse, studies have focused on the mechanism of collapse, the morphological characteristics of collapse, the control of collapse, amongst other criteria. Because the surface tension of water results in wood cell collapse, the shape of collapsed cells should be recovered after the liquid tension disappears. Therefore, pretreating green timber (such as pre-heating, pre-steaming, microwave treatment, pre-freezing, or boiling) prior to drying results in the modification of wood cell tissue and inhibits the conditions for collapse. Thus, there is improved wood permeability, drying rate, shortened drying time, as well as reduced collapse during the drying process. In addition, applying process control in regards to a suitable drying schedule (especially the drying temperature), relative humidity, drying time, intermittent drying process, combined drying technology, etc., tends to reduce the amount of collapse and improve drying quality. Reconditioning, such as steaming during the drying process, can aid collapse recovery. Generally, reconditioning or other treatment can help recover 50% of the collapse.

Plasticity-mediated collapse and recrystallization in hollow copper nanowires: a molecular dynamics simulation.

We study the thermal stability of hollow copper nanowires using molecular dynamics simulation. We find that the plasticity-mediated structural evolution leads to transformation of the initial hollow structure to a solid wire. The process involves three distinct stages, namely, collapse, recrystallization and slow recovery. We calculate the time scales associated with different stages of the evolution process. Our findings suggest a plasticity-mediated mechanism of collapse and recrystallization. This contradicts the prevailing notion of diffusion driven transport of vacancies from the interior to outer surface being responsible for collapse, which would involve much longer time scales as compared to the plasticity-based mechanism.

Effect of Drying Conditions on the Collapse-prone Wood of Eucalyptus urophylla

Collapse is considered one of the most severe defects that can occur during the drying of eucalyptus, resulting in drying degradation. Liquid tension is one of the reasons for the collapse. Some transient-collapse cells can be recovered upon the disappearance of liquid tension, when moisture content is reduced during the drying process. How to control collapse and help its recovery are key factors of drying technology. This supports the introduction of a kind of sequential drying technology to the drying process. Thus, several intermittent drying procedures were used in this study. Measurements of shrinkage and collapse were made on Eucalyptus urophylla under continuous drying as well as several kinds of intermittent drying. Key factors of the intermittent drying schedule, observed for their effect on collapse recovery, were the length of the drying periods and temperature during the intermittent periods. The microstructure of collapse under different drying schedules was examined at the cellular level using scanning electron microscopy (SEM). This confirmed that intermittent drying conditions can help collapsed cells recover more thoroughly than continuous drying conditions.

The Study on Cell Collapse and Recovery of Eucalyptus urophylla during Drying

To explore the collapse of eucalyptus wood cells during the drying process, continuous and intermittent drying were carried out on Eucalyptus urophylla. The shrinkage throughout the intermittent drying process was less than that of continuous drying. According to observations of cells made using scanning electron microscopy (SEM), there was a large difference in the degree of cell collapse between continuous and intermittent drying. Severe cell collapse was observed after freeze-drying at high moisture content, even after an intermittent drying process. It is clear that collapse recovery via intermittent drying was more extensive than in continuous drying. In particular, ray parenchyma and axial parenchyma recovered from collapse more than did wood fibers.

Structural bone graft for treatment of complicated distal radius fractures and bone defects

Objective To investigate the curative effect of structural bone graft in treatment of high energy injury-induced complicated distal radius fractures combined with articular surface collapse and comminuted epiphyseal bone defect. Methods The study involved 38 patients with distal radius fractures (AO classification, type C3) treated from January 2007 to October 2010.The patients were treated with temporary Kirschner wire fixation to recover the wrist articular surface, distal radius length and palmar tilt angle at the greatest possibility.According to the form of the bone defects, the iliac bone taken from three layers of the cortical bone was embedded in the subchondral bone to support the bone graft, and a small amount of cancellous bone graft was collected to fill the articular surface collapse as much as possible for anatomical reduction of the articular surface, and anatomical form of the distal radius was reconstructed.Modified Sarmiento Gartland and Werley evaluation systems were used to evaluate the articular function recovery. Results The follow-up lasted for 1-3.2 years, which showed no complications such as plate rupture or iatrogenic nerve blood vessels injuries.The fracture healing time was 15-22 weeks (mean 18.3 weeks).The wrist articular function in some patients obtained obvious improvement through functional rehabilitation training.According to the modified Gartland and Werley function evaluation systems, the curative effects reached excellence rate of 87％.During follow-up, there were two patients with high progressive loss in the height of the distal radius and two with articular surface collapse and severe carpal joint flexion and extension dysfunction. Conclusions The high energy injury-induced distal radius fractures with articular surface collapse and epiphyseal bone defect need recovery of the wrist articular surface, distal radius length and palmar tilt angle.Structural bone graft can effectively support the grafted bone and maintain the flatness of the radiocarpal articular surface, restore the anatomy of the distal radius and facilitate the functional recovery of the wrist. Key words: Radius fractures; Bone transplantation; Joints; Fracture healing

Delamination in Wood, Wood Products and Wood-Based Composites

<i>Delamination in Wood, Wood Products and Wood-Based Composites</i>

A hybrid multi-stage predictive model for supply chain network collapse recovery analysis: a practical framework for effective supply chain network continuity management

In this paper, we present a multi-stage hybrid model for analysing a supply chain network (SCN) collapse recovery possibility. In the first stage of the model, we analyse the ability of an SCN to fulfil its customers required due date (RDD). As soon as the SCN defaults to timely fulfil their customers RDD, the second stage of the model is triggered to measure the collapse recovery possibility (CRP) of the SCN. Then, we calculate the final collapse recovery possibility (FCRP) of the SCN. Since the operation times, customer demand and external supply of raw material are uncertain, we use fuzzy triangular numbers to estimate the value of foregoing parameters. Consequently, we employ fuzzy program evaluation and review technique (FPERT) to calculate the completion time of SCN operations. In the third stage, for the critical elements of the SCN obtained from FPERT, the SC simulator is developed to provide a dynamic view of the SC and assesses the impact of decisions recommended by the SC fuzzy models on SC performance. Moreover, an empirical example is presented to validate the effectiveness of the proposed model. Finally, we conduct sensitivity analysis on the parameters employed in the model to analyse the behaviour of each parameter.

Effect of pre-drying schedule ramping on collapse recovery and internal checking with Victorian Ash eucalypts

Matched sample boards from 20 quarter-sawn boards of Victorian Ash (Eucalyptus regnans F. Muell and E. delegatensis R.T. Baker) were dried using three different levels of ramped pre-drying schedules to investigate the effects of moisture gradients on collapse recovery and internal checking. Prior to reconditioning, most wet cores were found in highly collapsed boards with low density. Reducing the gradients in these boards is crucial for recovering collapse and closing internal checks. If time allows the boards to be equilibrated prior to steam reconditioning, a target mean moisture content of ≤20% with a moisture gradient of close to 5% (core to surface moisture content) is likely to recover slightly more collapse than targeting a mean moisture content close to ≥15%. However, if time or kiln restraints limit equilibration it is likely to be better to target a percentage moisture content of closer to 15% in order to ensure that the core to surface moisture gradients are below 8–10%. The slight reduction in collapse recovery with this second approach is less important than the possibility that collapse and internal checks in the centre of boards with wet cores will not be closed. Care needs to be used with this latter approach not to over-dry some boards, since moisture contents below 15% will progressively reduce collapse recovery. For boards within these moisture content guidelines, the application of heat, rather than moisture pick-up, appears to be the most important component of the steaming reconditioning process. Hence, steaming only needs to be undertaken for long enough to heat the core of the board close to the target temperature of 100°C. A simple method for estimating this heat-up time for different thicknesses and species was demonstrated based on a key dimensionless group for heat transfer, the heat-transfer Fourier number.

Presidential Address 2007: The end-Permian mass extinction — events on land in Russia

The mass extinction of life in the sea and on land 251 million years ago, at the Permian—Triassic boundary, was undoubtedly the largest mass extinction of all time. Sedimentological and geochemical evidence show that global temperatures rose, that there was extensive oceanic anoxia, and that there was massive erosion of sediment, especially soils, from the land. These phenomena might have been a consequence of the massive eruptions of the Siberian Traps, which produced carbon dioxide — a greenhouse gas — as well as acid rain, which killed plants and led to stripping of soils. Field work in Russia over the past decade has shown evidence for massive erosion at the boundary, and for the nature of ecosystem collapse and slow recovery after the event.

Numerical Simulation of the Gas Discharge in a Gas Peaking Switch

The gas discharge in a gas peaking switch was divided into three phases as gas breakdown, voltage collapse, and gaseous recovery. The development of the discharge was numerically simulated. Nitrogen and hydrogen at pressure ranging from 30 to 100 atm were chosen as working gases. The breakdown field of nitrogen is much higher than that of hydrogen, and a value of 4 MV/cm is achieved for a 0.6-mm nitrogen gap at the pressure of 100 atm. Depending strongly on the breakdown field, the rise time of the output pulse from the nitrogen gap is much shorter than that from the hydrogen gap. The shortest rise time of 108 ps for 0.6-mm nitrogen gap at the pressure of 100 atm is obtained. The gaseous recovery of the extinguished spark channel depends mainly on the recovery of gas density resulting from the falling of the channel temperature due to the axial heat flow out from the channel through the metal electrodes. Hydrogen is much better than nitrogen for gaseous recovery. Electrode material also plays an important role.

Effect of mean moisture content on the steam reconditioning of collapsed Eucalyptus regnans

Sixteen quarter-sawn boards (100 × 40 mm2) of regrowth Eucalyptus regnans (Mountain Ash) were conditioned to various moisture contents to investigate the effect of mean moisture content on collapse recovery. The results support the recommendation that boards should be reconditioned at a mean moisture content of between 15 and 20%. It is likely that the actual amount of collapse recovery was nearly as good for moisture contents up to about 25%. The main disadvantage with reconditioning boards with a moisture content of between 20 and 25% was the additional normal shrinkage that occurs because of the early reduction or removal of drying stresses. The samples in this study were dried under mild conditions for long periods of time to minimise the presence of moisture gradients.

Qualidade da secagem de madeira serrada de &lt;i&gt;Eucalyptus dunnii. &lt;/i&gt;

No presente estudo, foi avaliado o comportamento de secagem da madeira de Eucalyptus dunnii em estufa piloto convencional, utilizando-se três programas de secagem. Cada programa de secagem teve uma vaporização inicial (pré-vaporização) de 3 horas após uma hora de aquecimento inicial e uma vaporização intermediária de 5 horas para recuperação do colapso, quando a madeira se encontrava a 17% de umidade. Os resultados mostram que, entre os programas de secagem utilizados, somente o programa considerado o mais suave apresentou um bom resultado em termos de qualidade de madeira seca. Entre os defeitos encontrados estão 37,5% de colapso, 35% de encanoamento e 10% de rachaduras. Embora, desse total, somente 15% do colapso e encanoamento foram classificados como defeitos fortes.

Shrinkage and collapse in thin sections and blocks of Tasmanian mountain ash regrowth

Total collapse values from the green condition to various equilibrium moisture contents (EMC) were obtained by comparing shrinkage before reconditioning in matched blocks and sections of the wood of Eucalyptus regnans. It was shown that while collapse to 17% EMC comprised the largest portion of total collapse, a significant component, apparently caused by drying stress, developed below 17% EMC. Between 5% EMC and 0% moisture content a collapse recovery of some 1% occurred, seemingly because of changes in drying temperature. After reconditioning, collapse recovery was only partial and a high level of residual collapse remained. It was shown that collapse recovery was highest near the sapwood-heartwood boundary, while residual collapse was highest near the heartwood centre. While residual collapse was weakly negatively correlated with specific gravity, this relationship was not significant after adjustment was made for change in shrinkage after reconditioning in sections. All types of collapse were positively correlated with R-ratios calculated for blocks. However, relationships were not as well defined when R-ratios for sections were employed, the exception being for collapse below 17% EMC which was highly negatively correlated with R. The difference between shrinkage before reconditioning and shrinkage after reconditioning in sections, while totalling near zero, was positively correlated with specific gravity. It was demonstrated that this quantity could not constitute collapse in the traditional sense of collapse of the cell lumens. A possible association with moisture content of the material was discussed.

The Effect of Boiling Time on the Change in Green Wood Volume inEucalyptus regnansF. Muell.

The green volume of increment core segments of Eucalyptus regnans was shown to increase after boiling in water (hygrothermal recovery), the changes being quadratically related to the logarithm of the boiling time. Maximum changes were recorded after 8 to 16 minutes boiling, those times at which shrinkage after reconditioning was shown previously to be at a minimum and recovered collapse a maximum. In the heartwood it was demonstrated that, when boiling time was omitted from the regression analyses, changes in shrinkage after reconditioning after boiling and changes in percentage collapse recovery were, respectively, negatively and positively related to change in green volume.

Weight at birth in Vienna, Austria, 1865–1930

This study examines the relationship between weight at birth and socioeconomic influences in Vienna, Austria between 1865 and 1930, a period of industrial development followed by economic collapse and subsequent recovery. A random sample of maternity patients from the major hospital in Vienna was selected. Most patients were of low social and economic status. All live, singleton infants weighing 1500 g or more were included in the study. Multiple regression analysis reveals that ethnicity, religion and marital status did not influence birth weight variations and that sex, maternal age and birth order were strongly correlated with variations in birth weight means. It further reveals that the socioeconomic variables: occupation, season and year of birth, the length of a woman's stay in hospital prior to delivery and residential address were correlated with mean birth weight variations. Linear regression analysis suggests a moderately strong relationship between short-term fluctuations in the cost of living and mean birth weight.