Evacuation experiments in a virtual reality high‐rise building: exit choice and waiting time for evacuation elevators

The egress strategy in high‐rise buildings has traditionally been based on the sole use of stairs for evacuation. However, it is becoming more common to include evacuation elevators in the egress strategy in high‐rise buildings. Traditionally, evacuation elevators have not been allowed as an evacuation route, and people have been instructed to not use elevators in case of fire. This means that people might still not consider evacuation elevators even if they are designed to be safe in case of fire. Even if people choose evacuation elevators, they might not be willing to wait very long for an elevator to arrive. Virtual reality (VR) experiments were conducted to study exit choice and the waiting time for evacuation elevators in high‐rise buildings. The experiment was performed in a VR lab with a VR model of an existing high‐rise building. Results suggest that a simple way‐finding system using green flashing lights can influence people to more likely choose the elevator as their first evacuation choice. The results also show that the general trend is that people wait for either a limited time (<5 min) or a long time (>20 min). Copyright © 2015 John Wiley & Sons, Ltd.     

关于高层自动喷水灭火系统几个注意的问题

分析了在作用面积内自动喷水系统的5种喷头的不同布置间距条件下系统的设计流量,设计流量为强度面积法计算的1.66～3.0倍,其比例参数可用于设计。此外,分析了高区为标准层、低区为带裙楼的公共设施层的商务写字楼和宾馆高层建筑自动喷水灭火系统的设计流量特点和常规选择消防主泵存在的问题,提出以低区工况选泵,按高区工况校核的选泵方法,并给出该法适用范围,同时介绍了水力报警阀、喷头作用水头和泄水装置设置的有关问题。     

Preparation and high‐temperature behavior of HfC–SiC nanocomposites derived from a non‐oxygen single‐source‐precursor

A single‐source precursor for the preparation of HfC‐SiC ceramics was synthesized via a Grignard reaction using bis(cyclopentadienyl)hafnium(IV) dichloride, trans‐1,4‐dibromo‐2‐butene, and (chloromethyl)trimethylsilane as raw materials. The composition, structure, pyrolysis process and high‐temperature behavior of the precursor were investigated. The results show that the precursor with a backbone comprising Hf–C, Si–C and CH=CH groups exhibits good solubility in common solvents, such as tetrahydrofuran, dimethylbenzene, and chloroform. Pyrolysis of the precursor at 1000°C yielded a microcrystalline HfC phase with a ceramic yield of 63.86 wt%. The pyrolytic products at 1600°C were HfC–SiC nanocomposite ceramics, which exhibited good thermal stability up to 2400°C. The formation of a (Hf,Si)C solid‐solution would be beneficial for densification during the sintering process. The non‐oxygen structure, high ceramic yield, homogeneous composition and excellent high‐temperature behavior of the pyrolytic products make the as‐prepared precursor a promising material for the preparation of high‐performance ultra‐high‐temperature ceramics.     

Electric self‐heating behavior of acetylene carbon black filled high‐density polyethylene composites

The electric self‐heating behavior of carbon black (CB) filled high‐density polyethylene (HDPE) was studied in relation to the time‐dependent current and surface temperature under various voltages and to the voltage‐dependent surface temperature at electric–thermal equilibrium. The resistance increase due to self‐heating restricts the current flow through the sample and thus stabilizes the electric power and the self‐heating temperature to their saturation values, which vary with the voltage. A simple phenomenological model shows that self‐heating at electric‐thermal equilibrium is involved in the initial resistance, the electric field induced positive temperature coefficient (PTC) transition and the heat dissipation. The influences of annealing and irradiation crosslinking on the self‐heating behavior are discussed. Copyright © 2004 Society of Chemical Industry     

Dynamic mechanical behavior of atactic and high‐impact polystyrene

Results of the dynamic mechanical behavior of atactic polystyrene (PS) and high‐impact polystyrene (HIPS) for temperatures between 300 and 425 K at a frequency of the order of 50 kHz are presented. The storage Young's modulus, (E′), of the HIPS is lower than the PS value, being the relationship between them a function of the rubber phase volume fraction, independent of the measurement frequency. The glass transition temperature (T_g) of HIPS is shifted to lower temperature in respect to the PS. The γ relaxation appears at 308 K in PS at 50 kHz, while it seems to move toward lower temperatures in the HIPS. Both shifts are attributed to the presence of mineral oils in the HIPS. The values of E′, T_g, and the temperature of the γ relaxation at 50 kHz are discussed within the scope of the theory of viscoelasticity. Finally, the effect of thermal treatments, using different annealing times, on the behavior of both materials is shown. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 865–873, 2000     

Power draw of a high‐Shear homogenizer

The power draw of a high‐shear rotor‐stator homogenizer has been characterized in laminar, transitional, and turbulent operation. The power draw is comprised of two components — that associated with mixing and that associated with a bushing and bearings in the device. In turbulent operation, the mixing power draw is influenced primarily by pumping mode (up‐ or down‐pumping), and to a lesser extent, by vessel baffling and other geometric parameters. Mixing power draw can be characterized in terms of power number across the Reynolds number spectrum if an empirical Froude number correction is applied.     

Studies on the kinetics of orientation and crystallization of nylon‐66 during high‐speed melt spinning

A new way of applying on‐line experimental data and basic theory to study the mechanism of orientation of a high‐speed melt spinning process is described. The relationship of birefringence and stress for Nylon‐66 was developed to understand the phenomena in the spinning line. The value of birefringence along the spinning line was calculated by various models to predict the orientation change. By comparison of the model prediction and on‐line experimental birefringence, a suitable mechanical model to simulate the change of the profiles along the spinning line was chosen, and the structural development mechanism is discussed. The results show that the orientation mechanism of high‐speed melt spinning of Nylon‐66 is determined by deformation and deformation rate along the spinning line. For Nylon‐66, molecular and crystal orientations develop independently and are controlled by the rotation of crystals and chain segments in the deformation field. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3157–3163, 2001     

Necking behavior in high‐speed melt spinning of poly(ethylene terephthalate)

The necking behavior in the high‐speed melt‐spinning process of poly(ethylene terephthalate) (PET) was analyzed using a mathematical simulation under a nonisothermal condition. A constitutive model into which the strain‐rate dependence of viscosity and the strain‐hardening effect are incorporated was used. Based on the simulated results, the cause of a local reduction of apparent viscosity was found to be due mainly to high strain rate. Also the onset of crystallization, if it occurred, was found to happen near the end of the neck. In addition, with no crystallization involved, the necking can still occur. The deformation process in high‐speed spinning of PET was found to consist of two regions along the spin line: a Newtonian flow region and a rubberlike deformation region. The necking behavior is discussed here in terms of strain‐rate sensitivity and strain‐hardening parameter. As a result, a criterion for the onset of stable necking has been obtained. The necking behavior does not seem to be essentially different from that in cold drawing. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 446–456, 2000     

Structure development and property changes in high‐density polyethylene/calcium carbonate blends during pan‐milling

A new self‐designed mechanochemical reactor, inlaid pan‐mill, was used in studying high density polyethylene (HDPE) and calcium carbonate (CaCO₃) blends. The effects of CaCO₃ on the crushing and structure of HDPE matrix and the properties of HDPE/CaCO₃ blends were investigated. Scanning electron microscopy, Fourier transformed IR spectroscopy, dynamical mechanical testing analysis, capillary rheometer, and Instron material testing system were used to characterize the structure of HDPE and evaluate the properties of HDPE/CaCO₃ blends. The introduction of calcium carbonate during milling improved milling efficiency, and time needed for each cycle was greatly reduced. Oxygen‐containing groups on HDPE chains, which were produced during milling, increased interfacial interactions and improved the dispersion and distribution of calcium carbonate particles in HDPE/CaCO₃ blends. Rheological, thermal, and mechanical properties were also improved. The elongation at break of milled blends with high concentrations of calcium carbonate was significantly higher than that of unmilled blends. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1459–1464, 1999     

Fine‐structure and physical properties of polyethylene fibers in high‐speed spinning. I. Effect of melt‐flow rate in the high‐density polyethylene

High‐density polyethylene (HDPE) fibers, obtained from a melt‐flow rate (g/10 min) of 11 and 28, was produced by a high‐speed melt‐spinning method in the range of take‐up velocity from 1 to 8 km/min and from 1 to 6 km/min, respectively. The change of fiber structure and physical properties with increasing take‐up velocity was investigated through birefringence, wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), a Rheovibron, and a Fafegraph‐M. With an increase in take‐up velocity, the birefringence showed a sigmoidal increase, which has distinct changes in the range of 1–5 km/min. Throughout the whole take‐up velocities, the birefringence of HDPE(11) was higher than that of HDPE(28). With increasing take‐up velocity, the crystalline orientation was transformed from a‐axis orientation to c‐axis orientation. These crystalline relaxations are confirmed by the tan δ peak of high‐speed spun HDPE fibers. The intensity of the crystalline relaxation peak decreases with increasing take‐up velocity in both HDPE(11) and HDPE(28). As above, the crystalline relaxation peaks shift to lower temperature with increasing take‐up velocity. With increasing take‐up velocity, the ultimate strain decreases while both specific stress and the initial modulus increase. The mechanical behavior may be closely related to, as investigated by birefringence, orientation of the amorphous region, etc., the take‐up velocity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1182–1195, 2000     

Improvement of the tribological behavior of ultra‐high‐molecular‐weight polyethylene by incorporation of poly (phenyl p‐hydroxyzoate)

Ultra‐high‐molecular‐weight polyethylene/poly (phenyl p‐hydroxyzoate) composites (coded as UHMWPE/PPHZ) were prepared by compression molding. The effects of the poly (phenyl p‐hydroxyzoate) on the tribological properties of the UHMWPE/PPHZ composites were investigated, based on the evaluations of the tribological properties of the composites with various compositions and the examinations of the worn steel surfaces and composites structures by means of scanning electron microscopy and transmission electron microscopy. It was found that the incorporation of the PPHZ led to a significant decrease in the wear rate of the composites. The composites with the volume fraction of the PPHZ particulates within 45% ～ 75% showed the best wear resistance. The friction coefficient of the UHMWPE/PPHZ composites decreased with increasing load and sliding velocity, while the wear rates increased with increasing load. This was attributed to the enhanced softening and plastic deformation of the composites at elevated load or sliding velocity. The UHMWPE/PPHZ composites of different compositions had differences in the microstructures and the transfer film characteristics on the counterpart steel surface as well. This accounted for their different friction and wear behaviors. The transfer film of the UHMWPE/PPHZ composites appeared to be thinner and more coherent, which was largely responsible for their better wear resistance of t composite than the UHMWPE matrix. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2336–2343, 2005     

Fatty acid profile changes during orange juice‐milk beverage processing by high‐pulsed electric field

High‐intensity pulsed electric fields (HIPEF) is an emerging non‐thermal food preservation technology which has the potential to pasteurize pumpable liquid foods. Its application is being studied to evaluate it as potential alternative or complementary process to thermal pasteurization. Orange juice‐milk beverage with added bioactive components is a ready‐to‐drink beverage developed as an alternative to traditional soft drinks. In the present work, two HIPEF treatments (35 and 40 kV/cm) and six different treatment times (from 40 to 180 µs) were evaluated to assess their effect on the fatty acid profile of an orange juice‐milk beverage fortified with n‐3 fatty acids and oleic acid. The effect of HIPEF treatment on various physicochemical properties of the beverages: pH, °Brix, hydroxymethylfurfural or peroxide index was also determined. After HIPEF treatment, non‐significant changes in the contents of saturated fatty acids, monounsaturated fatty acids or polyunsaturated fatty acids were observed. Neither peroxides nor intolerable levels of furfurals were detected. Only a small reduction in fat content (p <0.05) was found. In conclusion, HIPEF can be proposed as an alternative preservation technology due to these minimal changes which are negligible from the nutritional point of view.     

High‐temperature and high‐pressure ethylene polymerization using a cationic activated metallocene catalytic system

BACKGROUND: Normally, olefin polymerization via metallocene‐based catalysis occurs under mild conditions. However, most technology developed for polyolefin production is designed for more severe temperature and pressure processes. Attaining more thermally stable metallocene systems for industrial applications is an important challenge for researchers. RESULTS: A systematic study of ethylene homopolymerization at higher temperatures and pressures, employing the ternary system Ph₂C(Cp)(Flu)ZrCl₂/PhNHMe₂B(C₆F₅)₄/(i‐Bu)₃Al, is presented The optimal activity for this system is achieved with a Zr/B/Al molar ratio of 1/6/250 and a temperatures of around 130 °C. However, the amount of activator strongly affects the molecular weight and the polydispersity of the polymers produced. Polyethylene produced with Zr/B/Al molar ratios between 1/2/250 and 1/6/250 show no significant difference in their temperature of fusion (T_m) and their crystallinity (X_c). In contrast, in the presence of activator amounts higher than 1/6/250, both the temperature of fusion and polymer crystallinity undergo a steep decrease. All polymers presented lamellar morphology when the activator was present, and an amorphous aspect when the activator was not employed. CONCLUSION: The presence of the activator is essential for thermal stabilization of the catalytic system. Variation of the Zr/B/Al ratio leads to modifications of the catalytic activity as well as to the properties of the polymers synthesized. Copyright © 2008 Society of Chemical Industry     

Study on the high‐temperature behavior and rehydration characteristics of hardened cement paste

The high‐temperature behavior and rehydration characteristics of the hardened cement paste and their mechanisms have been studied in this paper. X‐ray diffraction and thermogravimetry are used to establish the effect of elevated temperatures on the mineralogical changes that occurred in the hardened cement paste. The change of microstructure was characterized by scanning electron microscopy. The results showed that with the temperature increased, the compressive strength of hardened cement paste first increased and then decreased. According to micromeasurements, at 400°C, the porosity and average pore diameter of hardened cement paste increased slightly, while at 800°C, the porosity and average pore diameter of hardened cement paste increased sharply. When hardened cement paste was cured after exposing to 400°C, its pore structure and phase composition had no change, while when hardened cement paste was cured after exposing to 800°C, there are new hydration products, and its pore structure may be finer, but it cannot fully recover to the original state. Copyright © 2014 John Wiley & Sons, Ltd.     

Two‐step degradation of high‐density polyethylene during multiple extrusion

Ensuing our recent studies on polyethylene stabilization,^1,2 further multiple extrusion experiments were carried out with a high‐density polyethylene (HDPE) polymer containing various amounts of a sterically hindered phenolic antioxidant. Discoloration, thermoxidative stability, and melt flow index (MFI) retention were measured by standard techniques; the functional group content of the polymer was determined by Fourier transform infrared (FTIR) spectroscopy, and rheological, as well as mechanical properties, were also measured. The results indicated that degradation and stabilization reactions take place according to two different mechanisms in the first and subsequent processing steps, respectively. Color development could be described well by the simple first‐order overall reaction kinetics proposed earlier, and color change could be related to the stability of the polymer. The existence of general correlations among the properties proved that all chemical reactions are interrelated. The reactions of the stabilizer lead to color development, while those of the polymer to a modification of its molecular architecture, which determines the rheological and mechanical characteristics of the product. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1596–1605, 1999     

Effect of initial crystallinity on the response of high‐density polyethylene to high‐energy radiation

Samples of each of two high‐density polyethylenes with various initial degrees of crystallinity, but otherwise identical, were exposed under a vacuum to moderate doses of gamma irradiation. The results indicate that, for otherwise initially identical polymer samples, the dose required to reach the gel point increases with increase of the initial degree of crystallinity. Above the critical dose for gelation, the gel content decreases with higher degrees of crystallinity at equal radiation doses. The mechanical behavior of the polymers changed progressively from ductile to brittle as the crystallinity was increased. The extensibility of originally ductile samples decreases with increasing radiation dose. The irradiation of samples having intermediate behavior produces a change to ductile behavior. Mechanical behavior is not modified substantially when brittle samples are irradiated. The initial modulus is little altered by irradiation, while the yield stress shows a slight increase with irradiation. The mechanical properties, such as draw ratio at break and ultimate tensile stress, decrease with dose in ductile samples. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1375–1384, 1999     

Subgrid scale scalar variance in high‐Schmidt‐number turbulence

The subgrid scale (SGS) variance for a high‐Schmidt‐number passive scalar of Sc >> 1 is measured using a high‐resolution planar laser‐induced fluorescence technique in a grid‐generated turbulent liquid flow, and the values of the model coefficients in the scale‐similarity model and the scalar‐gradient model used for estimating the SGS scalar variance are experimentally evaluated. The results show that for both models, the measured values are much larger than the well‐known values obtained in the previous studies done for non‐high‐Sc scalars of Sc ? 1. Similarly, the measured value of the model coefficient in the scalar‐gradient model tends to be larger than the value estimated by the dynamic procedure. The increases in the measured values of the model coefficients for the high‐Sc scalar can be explained by the presence of the viscous‐convective range showing a nearly (?1)‐slope in the high‐wavenumber range of the power spectrum of concentration fluctuation. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Preparation of ketoprofen‐loaded high‐molecular‐weight poly(vinyl alcohol) gels

High‐molecular‐weight atactic poly(vinyl alcohol) (a‐PVA) gels loaded with (R,S)‐2‐(3‐benzoylphenyl)propionic acid (ketoprofen) were prepared from 5, 6, 7, and 8 g/dL solutions of a‐PVA with a number‐average degree of polymerization of 4000 in an ethylene glycol/water mixture with an aging method to identify the effect of the initial polymer concentration on the swelling behavior, morphology, and thermal properties of a‐PVA gels. Then, the release behavior of ketoprofen from a‐PVA gels was investigated. As the polymer concentration decreased, the ability for network formation decreased, and the degree of swelling of the a‐PVA gels increased. In addition, the enthalpy increased with an increase in the a‐PVA concentration, but the melting temperatures of the gels prepared at different initial polymer concentrations were the same; this indicated that tighter gel networks would be formed by a higher polymer chain density. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Residual response of fire‐damaged high‐strength concrete beams

This paper presents results from an experimental study on residual capacity of fire‐damaged high‐strength concrete (HSC) beams. Four reinforced concrete (RC) beams, fabricated with HSC, were first subject to structural loading and fire exposure with a distinct cooling phase and then loaded to failure upon cooldown to ambient conditions to evaluate residual capacity. Temperatures, deflections, and spalling in the beams were monitored during heating and cooling phases of fire exposure. Further, residual capacity, strains at critical section, and crack patterns (failure mode) of fire‐damaged beams were recorded during residual capacity tests. Results from experiments indicate that the load level during fire exposure, duration of heating phase, rate of cooling, extent (type) of spalling, and duration of postcooling storage influence residual deformations and also residual capacity of RC beams. Further, fire‐damaged HSC beams can recover 40% to 70% of their flexural capacity with respect to their room temperature design capacity provided they survive the entire duration of fire exposure.