bluuebunny/crossref_metadata_2025 huggingface dataset:
Penny Wise and Effect Size Foolish
Authors: Duncan Greg J. , Magnuson Katherine
Published: September 2007

ABSTRACT—
Although much developmental research is focused on basic science, some applied studies aspire to concrete policy recommendations. We suggest several steps that these studies might take to increase their chances of success. Scaling policy‐relevant variables in useful ways is a simple example. Most important is providing even rough estimates of the costs and benefits of recommended policy changes. Cost–benefit calculations are particularly useful because they indicate whether a policy or a program is likely to be an effective investment of public funds.
The Label Mental Retardation Involves More Than an IQ Score: A Commentary on Kanaya and Ceci (2007)
Authors: Hagen John
Published: September 2007

ABSTRACT—
Labeling a child as mentally retarded (MR) has been shown to be a complex process. A particular score on an IQ test is a necessary but not sufficient criterion. The Flynn effect, as described by Kanaya and Ceci (2007), does affect the labeling process. Other considerations in this process include the metrics of IQ tests and the child’s sex, race, socioeconomic status, and geographic residence. The usefulness of IQ test scores continues to be debated by scholars and practitioners, yet current practice regularly utilizes the tests as well as other factors in MR labeling.
Ex Vivo Fluorescence Imaging of Normal and Malignant Urothelial Cells to Enhance Early Diagnosis
Authors: Steenkeste Karine , Lécart Sandrine , Deniset Ariane , Pernot Pascal , Eschwège Pascal , Ferlicot Sophie , Lévêque‐Fort Sandrine , Briandet Romain , Fontaine‐Aupart Marie‐Pierre
Published: September 2007

Urinary cytology is a noninvasive and unconstraining technique for urothelial cancer diagnosis but lacks sensitivity for detecting low‐grade lesions. In this study, the fluorescence properties of classical Papanicolaou‐stained urothelial cytological slides from patients or from cell lines were monitored to investigate metabolic changes in normal and tumoral cells. Time‐ and spectrally‐resolved fluorescence imaging was performed at the single cell level to assess the spectral and temporal properties as well as the spatial distribution of the fluorescence emitted by urothelial cells. The results reveal quite different fluorescence distributions between tumoral urothelial cells, characterized by a perimembrane fluorescence localization, and the normal cells which exhibit an intracellular fluorescence. This is not caused by differences in the fluorescence emission of the endogenous fluorophores NAD(P)H, flavoproteins or porphyrins but by various localization of the EA 50 Papanicolaou stain as revealed by both the spectral and time‐resolved parameters. The present results demonstrate that the use of single‐cell endofluorescence emission of Papanicolaou‐stained urothelial cytological slides can allow an early ex vivo diagnosis of low‐grade bladder cancers.
Photophysical Properties of Ricin
Authors: Gaigalas A.K. , Cole K.D. , Bykadi S. , Wang Lili , DeRose Paul
Published: September 2007

The molar absorption coefficient of ricin in phosphate‐buffered saline (PBS) at 279 nm was measured as (93 900 ± 3300) L mol−1 cm−1. The concentration of ricin was determined using amino acid analysis. The absorption spectrum of ricin was interpreted in terms of 69% contribution from absorption by tryptophan residues and 31% contribution from absorption by tyrosine residues. The total dipole strength of the ricin band at 280 nm was determined to be (147 ± 8) D2 and was consistent with the combined dipole strengths of 10 tryptophan ([11.7 ± 1.0] D2) and 23 tyrosine ([1.4 ± 0.2] D2) residues. The structure of ricin was used to determine the coupling of the tryptophan residues in ricin. The maximum interaction energy was found to be 424 cm−1/ɛ while the average interaction between any two pairs of tryptophan residues was approximately 18 cm−1/ɛ. In this study, ɛ is the dielectric constant inside the protein. The fluorescence from ricin, excited at 280 nm, was dominated by fluorescence from tryptophan residues suggesting the presence of energy transfer from tyrosine to tryptophan residues. The absorbance and fluorescence of ricin increased slightly when ricin was denatured in a high concentration of guanidine. Irreversible thermal unfolding of ricin occurred between 65°C and 70°C.

(D = 3.3364*10−30 Cm, not SI unit, convenient unit for the magnitude of the electric dipole moment of molecules.)
Isovitexin‐2″‐O‐β‐[6‐O‐E‐p‐coumaroylglucopyranoside] from UV‐B irradiated Leaves of Rice, Oryza sativa L. Inhibits Fertility of Helicoverpa armigera
Authors: Caasi‐Lit Merdelyn T. , Tanner Gregory J. , Nayudu Murali , Whitecross Malcolm I.
Published: September 2007

UV‐B irradiated rice leaves (Oryza sativa L.) contained four closely related flavonoids, with either an isoorientin or isovitexin aglycone. These flavonoids have previously been purified and characterized, and were added to artificial diets of the African bollworm (Helicoverpa armigera Hübner) at 0.1× concentration found in irradiated rice leaves. Consumption of different diets had relatively small effects on laval, pupal and adult duration, weight and survival, indicating the insects lived near normal life cycles on all diets. However, one of the compounds, flavonoid IIa, isovitexin‐2″‐O‐β‐[6‐O‐E‐p‐coumaroylglucopyranoside], dramatically reduced the number of fertile eggs laid to 7% of control insects (P < 0.001) when added to insect diets at 18 nmol gFW−1 (14 ppm). A similar antifertility effect was observed when only the male partner consumed diet containing flavonoid IIa, indicating that the reduced fertility may be male specific. In contrast, the fecundity and fertility of insects eating diets containing the closely related flavonoids, isoorientin‐2″‐O‐β‐[6‐O‐E‐p‐coumaroylglucopyranoside] or isoorientin‐2″‐O‐β‐[6‐O‐E‐p‐feruloylglucopyranoside], were not significantly different to control diets.
Seasonal Erythemal UV Doses in Belo Horizonte, Brazil
Authors: Silva Abel A. , Gabrich Lívia L. P.
Published: September 2007

The ultraviolet radiation (UVR) emitted by the Sun causes many effects on the biosphere. On human beings they vary from the benefit of vitamin D synthesis to the harm of skin cancer induction. The biological dose depends on the effect, the exposure time to the Sun and the amount of UVR received. In this work we show that the measured incidence of erythemal dose (ED) in Belo Horizonte (19.92°S, 43.94°W, 858 m a.s.l., Brazil) for a cloudless day can vary from 7503 to 2926 J m−2 in the summer–winter seasonal variation. In addition, supposing a linear relationship between the ED and the geophysical parameters of solar zenith angle cosine (cos(SZA)), column ozone and reflectivity from the ozone monitoring instrument overpass measurements, a model for the forecast of UVR incidence on a monthly‐based period is developed. From this an annual ED of 1 451 099 J m−2 is obtained.
Effect of Photosensitizer Dose on Fluence Rate Responses to Photodynamic Therapy†
Authors: Wang Hsing‐Wen , Rickter Elizabeth , Yuan Min , Wileyto E. Paul , Glatstein Eli , Yodh Arjun , Busch* Theresa M.
Published: September 2007

Photodynamic therapy (PDT) regimens that conserve tumor oxygenation are typically more efficacious, but require longer treatment times. This makes them clinically unfavorable. In this report, the inverse pairing of fluence rate and photosensitizer dose is investigated as a means of controlling oxygen depletion and benefiting therapeutic response to PDT under conditions of constant treatment time. Studies were performed for Photofrin‐PDT of radiation‐induced fibrosarcoma tumors over fluence rate and drug dose ranges of 25–225 mW cm−2 and 2.5–10 mg kg−1, respectively, for 30 min of treatment. Tumor response was similar among all inverse regimens tested, and, in general, tumor hemoglobin oxygen saturation (SO2) was well conserved during PDT, although the highest fluence rate regimen (225 mW × 2.5 mg) did lead to a modest but significant reduction in SO2. Regardless, significant direct tumor cell kill (>1 log) was detected during 225 mW × 2.5 mg PDT, and minimal normal tissue toxicity was found. PDT effect on tumor oxygenation was highly associated with tumor response at 225 mW × 2.5 mg, as well as in all other regimens tested. These data suggest that high fluence rate PDT can be carried out under oxygen‐conserving, efficacious conditions at low photosensitizer dose. Clinical confirmation and application of these results will be possible through use of minimally invasive oxygen and photosensitizer monitoring technologies, which are currently under development.
Assessing Welfare Reform, Over a Decade Later
Authors: Kissane Rebecca Joyce , Krebs Richard
Published: September 2007

It has now been over a decade since the passage of the 1996 welfare reform legislation (Personal Responsibility and Work Opportunity Reconciliation Act). In this paper, we synthesize the expansive literature on how welfare reform has affected poor families and nonprofit agencies that serve them. In particular, we explore state variation in welfare policies and the dramatic declines in welfare caseloads. We also investigate the employment, earnings, and levels of material hardships among current and former welfare recipients. Moreover, we examine what we know about welfare reform's impact on marriage, nonmarital childbearing, and child well‐being. Lastly, we report on how welfare reform has affected nonprofit agencies that serve poor families. We are left with a complex account of the impacts of welfare reform that reveals both positive developments in a number of areas and a great deal of remaining challenges.
Clinicopathological and prognostic features of primary clear cell carcinoma of the liver
Authors: Liu Zhisheng , Ma Weidong , Li Huikai , Li Qiang
Published: September 2007

Aim:  Primary clear cell carcinoma of the liver (PCCCL) is a subgroup of primary hepatocellular carcinoma (HCC), pathologically characterized by diffuse clear cells of the tumor, showing a clear cytoplasm that does not stain with hematoxylin–eosin. At present, its clinicopathological and prognostic features are not fully clarified. This study aims to clarify the clinicopathological and prognostic features of PCCCL.

Methods:  The clinicopathological data of 43 patients with PCCCL treated with hepatectomy in our hospital from January 1999 to December 2003 were retrospectively analyzed.

Results:  The χ2‐test showed a positive rate of hepatitis C virus (HCV) infection and capsule formation in the PCCCL group, which was markedly higher than in the common type HCC (CHCC) group (P = 0.000 and P = 0.005). Meanwhile, the vascular invasion rate was notably lower in the PCCCL group, but there were no significant differences between the twogroups (P = 0.129). The Kaplan–Meier method showed that the 1‐, 3‐, and 5‐year survival rates were significantly higher in the PCCCL group than in the CHCC group (P = 0.021). The prognosis of patients in the PCCCL group was related to capsule formation, vascular invasion, liver cirrhosis, and clear cell ratio. The 1‐, 3‐, and 5‐year survival rates were markedly higher in the group with a higher clear cell ratio than in the group with a lower clear cell ratio (P = 0.011).

Conclusion:  The notable clinicopathological features of the patients in the PCCCL group included a higher rate of HCV infection, capsule formation, and a lower rate of vascular invasion. The prognosis was better than that of the patients in the CHCC group and related to the ratio of clear cells.
Rat motoneuron properties recover following reinnervation in the absence of muscle activity and evoked acetylcholine release
Authors: Bichler Edyta K. , Carrasco Dario I. , Rich Mark M. , Cope Timothy C. , Pinter Martin J.
Published: September 2007

Available evidence supports the idea that muscle fibres provide retrograde signals that enable the expression of adult motoneuron electrical properties but the mechanisms remain unknown. We showed recently that when acetylcholine receptors are blocked at motor endplates, the electrical properties of rat motoneurons change in a way that resembles changes observed after axotomy. This observation suggests that receptor blockade and axotomy interrupt the same signalling mechanisms but leaves open the possibility that the loss of muscle fibre activity underlies the observed effects. To address this issue, we examined the electrical properties of axotomized motoneurons following reinnervation. Ordinarily, these properties return to normal following reinnervation and re‐activation of muscle, but in this study muscle fibre activity and evoked acetylcholine release were prevented during reinnervation by blocking axonal conduction. Under these conditions, the properties of motoneurons that successfully reinnervated muscle fibres recovered to normal despite the absence of muscle fibre activity and evoked release. We conclude that the expression of motoneuron electrical properties is not regulated by muscle fibre activity but rather by a retrograde signalling system coupled to activation of endplate acetylcholine receptors. Our results indicate that spontaneous release of acetylcholine from regenerated motor terminals is sufficient to operate the system.
The pontine REM switch: past and present
Authors: Fuller Patrick M. , Saper Clifford B. , Lu Jun
Published: September 2007

Rapid eye movement (REM) sleep is a behavioural state characterized by activation of the cortical and hippocampal EEG, rapid eye movements and muscle atonia. For the past 30 years, the most widely accepted neural circuitry model for the regulation of REM sleep has emphasized reciprocal inhibitory interactions between pontine brainstem monoaminergic and cholinergic neurons. In general support of the reciprocal interaction model, neuropharmacological studies have shown that cholinergic agonists promote REM sleep and muscarinic antagonists and monoamines inhibit REM sleep. It has nevertheless proven difficult to reconcile both the theoretical framework of this model and the pharmacological data with the fact that selective lesions of either cholinergic or monoaminergic (noradrenergic, serotoninergic or dopaminergic) nuclei in the brainstem have relatively limited effects on REM sleep. Recent work by our laboratory has revealed the presence of non‐cholinergic and non‐monoaminergic mutually inhibitory REM‐off and REM‐on areas in the mesopontine tegmentum that may form the neuroanatomical basis of the switching circuitry for REM sleep. These findings posit a REM switching circuitry model that is analogous to an electronic ‘flip‐flop’ switch. In this flip‐flop switch arrangement, GABAergic REM‐on neurons (located in the sublaterodorsal tegmental nucleus (SLD)) inhibit GABAergic REM‐off neurons (located in the ventrolateral periaqueductal grey matter (vlPAG) and lateral pontine tegmentum (LPT)) and vice versa. In the REM‐on area are two populations of glutamatergic neurons, the first of which projects to the basal forebrain and regulates EEG components of REM sleep and the second of which projects to the ventromedial medulla and spinal cord and regulates atonia during REM sleep. Our findings demonstrating independent pathways mediating atonia and the EEG components of REM provide a basis for their occasional dissociation in pathological states, e.g. REM sleep behaviour disorder.
Microscopic kinetic determinants of macroscopic currents: insights from coupling and uncoupling of GABAA receptor desensitization and deactivation
Authors: Bianchi Matt T. , Botzolakis Emmanuel J. , Haas Kevin F. , Fisher Janet L. , Macdonald Robert L.
Published: September 2007

The time course of inhibitory postsynaptic currents (IPSCs) reflects GABAA receptor deactivation, the process of current relaxation following transient activation. Fast desensitization has been demonstrated to prolong deactivation, and these processes have been described as being ‘coupled’. However, the relationship between desensitization and deactivation remains poorly understood. We investigated the ‘uncoupling’ of GABAA receptor macroscopic desensitization and deactivation using experimental conditions that affected these two processes differently. Changing agonist affinity preferentially altered deactivation, changing agonist concentration preferentially altered macroscopic desensitization, and a pore domain mutation prolonged deactivation despite blocking fast desensitization. To gain insight into the mechanistic basis for coupling and uncoupling, simulations were used to systematically evaluate the interplay between agonist affinity, gating efficacy, and desensitized state stability in shaping macroscopic desensitization and deactivation. We found that the influence of individual kinetic transitions on macroscopic currents depended not only on model connectivity, but also on the relationship among transitions within a given model. In addition, changing single rate constants differentially affected macroscopic desensitization and deactivation, thus providing parsimonious kinetic explanations for experimentally observed uncoupling. Finally, these findings permitted development of an algorithmic framework for kinetic interpretation of experimental manipulations that alter macroscopic current properties.
Chromophore switch from 11‐cis‐dehydroretinal (A2) to 11‐cis‐retinal (A1) decreases dark noise in salamander red rods
Authors: Ala‐Laurila Petri , Donner Kristian , Crouch Rosalie K. , Cornwall M. Carter
Published: September 2007

Dark noise, light‐induced noise and responses to brief flashes of light were recorded in the membrane current of isolated rods from larval tiger salamander retina before and after bleaching most of the native visual pigment, which mainly has the 11‐cis‐3,4‐dehydroretinal (A2) chromophore, and regenerating with the 11‐cis‐retinal (A1) chromophore in the same isolated rods. The purpose was to test the hypothesis that blue‐shifting the pigment by switching from A2 to A1 will decrease the rate of spontaneous thermal activations and thus intrinsic light‐like noise in the rod. Complete recordings were obtained in five cells (21°C). Based on the wavelength of maximum absorbance, λmax,A1= 502 nm and λmax,A2= 528 nm, the average A2 : A1 ratio determined from rod spectral sensitivities and absorbances was ∼0.74 : 0.26 in the native state and ∼0.09 : 0.91 in the final state. In the native (A2) state, the single‐quantum response (SQR) had an amplitude of 0.41 ± 0.03 pA and an integration time of 3.16 ± 0.15 s (mean ±s.e.m.). The low‐frequency branch of the dark noise power spectrum was consistent with discrete SQR‐like events occurring at a rate of 0.238 ± 0.026 rod−1 s−1. The corresponding values in the final state were 0.57 ± 0.07 pA (SQR amplitude), 3.47 ± 0.26 s (SQR integration time), and 0.030 ± 0.006 rod−1 s−1 (rate of dark events). Thus the rate of dark events per rod and the fraction of A2 pigment both changed by ca 8‐fold between the native and final states, indicating that the dark events originated mainly in A2 molecules even in the final state. By extrapolating the linear relation between event rates and A2 fraction to 0% A2 (100% A1) and 100% A2 (0% A1), we estimated that the A1 pigment is at least 36 times more stable than the A2 pigment. The noise component attributed to discrete dark events accounted for 73% of the total dark current variance in the native (A2) state and 46% in the final state. The power spectrum of the remaining ‘continuous’ noise component did not differ between the two states. The smaller and faster SQR in the native (A2) state is consistent with the idea that the rod behaves as if light‐adapted by dark events that occur at a rate of nearly one per integration time. Both the decreased level of dark noise and the increased SQR amplitude must significantly improve the reliability of photon detection in dim light in the presence of the A1 chromophore compared to the native (A2) state in salamander rods.
Anisotropic Heat Conduction Effects in Proton-Exchange Membrane Fuel Cells
Authors: Bapat Chaitanya J. , Thynell Stefan T.
Published: September 2007

The focus of this work is to study the effects of anisotropic thermal conductivity and thermal contact conductance on the overall temperature distribution inside a fuel cell. The gas-diffusion layers and membrane are expected to possess an anisotropic thermal conductivity, whereas a contact resistance is present between the current collectors and gas-diffusion layers. A two-dimensional single phase model is used to capture transport phenomena inside the cell. From the use of this model, it is predicted that the maximum temperatures inside the cell can be appreciably higher than the operating temperature of the cell. A high value of the in-plane thermal conductivity for the gas-diffusion layers was seen to be essential for achieving smaller temperature gradients. However, the maximum improvement in the heat transfer characteristics of the fuel cell brought about by increasing the in-plane thermal conductivity is limited by the presence of a finite thermal contact conductance at the diffusion layer/current collector interface. This was determined to be even more important for thin gas-diffusion layers. Anisotropic thermal conductivity of the membrane, however, did not have a significant impact on the temperature distribution. The thermal contact conductance at the diffusion layer/current collector interface strongly affected the temperature distribution inside the cell.
The Biot Model and Its Application in Viscoelastic Composite Structures
Authors: Zhang J. , Zheng G. T.
Published: September 2007

Application of viscoelastic materials in vibration and noise attenuation of complicated machines and structures is becoming more and more popular. As a result, analytical and numerical techniques for viscoelastic composite structures have received a great deal of attention among researchers in recent years. Development of a mathematical model that can accurately describe the dynamic behavior of viscoelastic materials is an important topic of the research. This paper investigates the procedure of applying the Biot model to describe the dynamic behavior of viscoelastic materials. As a minioscillator model, the Biot model not only possesses the capability of its counterpart, the GHM (Golla-Hughes-McTavish) model, but also has a simpler form. Furthermore, by removing zero eigenvalues, the Biot model can provide a smaller-scale mathematical model than the GHM model. This procedure of dimension reduction is studied in detail here. An optimization method for determining the parameters of the Biot model is also investigated. With numerical examples, these merits, the computational efficiency, and the accuracy of the Biot model are illustrated and proved.
The
Error Analysis of a Steady-State Thermal Conductivity Measurement Method With Single Constant
Temperature Region
Authors: Sun Ming-Tsung , Chang Chin-Hsiang
Published: September 2007

A method for steady-state thermal conductivity measurement with single constant temperature region has been developed. To better understand the accuracy of the method a numerical model is devised and verified by experimental results. The ratios of thermal conductivity derived from the temperature distribution solutions to that given in the numerical model are obtained and shown. They can be used to correct the systematic error of measurement introduced by the one-dimensional approximation. Finally, the measurement uncertainty due to misalignment of the temperature sensors and the limitation of sensing devices is also investigated. The numerical model is suitable for estimating the range of confidence in practical measurements.
A Fully Wet and Fully Dry Tiny Circular Fin Method for Heat and Mass Transfer Characteristics for Plain Fin-and-Tube Heat Exchangers Under Dehumidifying Conditions
Authors: Pirompugd Worachest , Wang Chi-Chuan , Wongwises Somchai
Published: September 2007

This study proposes a new method, namely the “fully wet and fully dry tiny circular fin method,” for analyzing the heat and mass transfer characteristics of plain fin-and-tube heat exchangers under dehumidifying conditions. The present method is developed from the tube-by-tube method proposed in the previous study by the same authors. The analysis of the fin-and-tube heat exchangers is carried out by dividing the heat exchanger into many tiny segments. A tiny segment will be assumed with fully wet or fully dry conditions. This method is capable of handling the plain fin-and-tube heat exchanger under fully wet and partially wet conditions. The heat and mass transfer characteristics are presented in dimensionless terms. The ratio of the heat transfer characteristic to mass transfer characteristic is also studied. Based on the reduced results, it is found that the heat transfer and mass transfer characteristics are insensitive to changes in fin spacing. The influence of the inlet relative humidity on the heat transfer characteristic is rather small. For one and two row configurations, a considerable increase of the mass transfer characteristic is encountered when partially wet conditions take place. The heat transfer characteristic is about the same in fully wet and partially wet conditions provided that the number of tube rows is equal to or greater than four. Correlations are proposed to describe the heat and mass characteristics for the present plain fin configuration.
Convective Heat Transfer in Open Cell Metal Foams
Authors: Salas Ken I. , Waas Anthony M.
Published: September 2007

Convective heat transfer in aluminum metal foam sandwich panels is investigated with potential applications to actively cooled thermal protection systems in hypersonic and re-entry vehicles. The size effects of the metal foam core are experimentally investigated and the effects of foam thickness on convective transfer are established. Four metal foam specimens are utilized with a relative density of 0.08 and pore density of 20 pores per inch (ppi) in a range of thickness from 6.4mmto25.4mm, in increments of approximately 6mm. An exact-shape-function finite element model is developed that envisions the foam as randomly oriented cylinders in cross flow with an axially varying coolant temperature field. A fully developed velocity profile is obtained through a semi-empirical, volume-averaged form of the momentum equation for flow through porous media, and used in the numerical analysis. The experimental results show that larger foam thicknesses produce increased heat transfer levels, but that this effect diminishes for thicker foams. The finite element simulations capture the thickness dependence of the heat transfer process and good agreement between experimental and numerical results is obtained for larger foam thicknesses.
An Experimental Study of the Friction Factor and Mass Transfer Performance of an Offset-Strip Fin Array at Very High Reynolds Numbers
Authors: Michna Gregory J. , Jacobi Anthony M. , Burton Rodney L.
Published: September 2007

Thermal-hydraulic performance data for offset-strip fin arrays are readily available in the range Re<10,000. However, in emerging applications in automotive and aerospace systems, where fan power is not a constraint and compactness is important, it may be desirable to operate offset-strip fin heat exchangers at very high Reynolds numbers. In this paper, friction factor and mass transfer performance of an offset-strip fin array at Reynolds numbers between 10,000 and 120,000 are characterized. A scale-model, eight-column fin array is used in pressure drop and naphthalene sublimation experiments, and the data are compared to predictions of performance given by available analytical models and extrapolations of the best available correlations. The friction factor data follow the correlation-predicted trend of decreasing monotonically as the Reynolds number is increased to 20,000. However, at higher Reynolds numbers, the friction factor increases as the Reynolds number increases and local maxima are observed in the data. Over the range investigated, the modified Colburn j factor decreases monotonically as the Reynolds number increases. For Reynolds numbers in the range 10,000<Re<120,000, well beyond that covered by state-of-the-art correlations, both the friction factor and Colburn j factor are roughly twice that predicted by extrapolating the best available correlations. The higher-than-predicted Colburn j factor at very high Reynolds numbers is encouraging for the use of offset-strip fin heat exchangers in emerging applications where compactness is of high importance.
Experimental Study and Genetic-Algorithm-Based Correlation on Shell-Side Heat Transfer and Flow Performance of Three Different Types of Shell-and-Tube Heat Exchangers
Authors: Wang Qiu-wang , Xie Gong-nan , Peng Bo-tao , Zeng Min
Published: September 2007

The heat transfer and pressure drop of three types of shell-and-tube heat exchangers, one with conventional segmental baffles and the other two with continuous helical baffles, were experimentally measured with water flowing in the tube side and oil flowing in the shell side. The genetic algorithm has been used to determine the coefficients of correlations. It is shown that under the identical mass flow, a heat exchanger with continuous helical baffles offers higher heat transfer coefficients and pressure drop than that of a heat exchanger with segmental baffles, while the shell structure of the side-in-side-out model offers better performance than that of the middle-in-middle-out model. The predicted heat transfer rates and friction factors by means of the genetic algorithm provide a closer fit to experimental data than those determined by regression analysis. The predicted corrections of heat transfer and flow performance in the shell sides may be used in engineering applications and comprehensive study. It is recommended that the genetic algorithm can be used to handle more complicated problems and to obtain the optimal correlations.
Expansion Ratio Effects on Three-Dimensional Separated Flow and Heat Transfer Around Backward-Facing Steps
Authors: Kitoh Aya , Sugawara Kazuaki , Yoshikawa Hiroyuki , Ota Terukazu
Published: September 2007

Direct numerical simulation methodology clarified the three-dimensional separated flow and heat transfer around three backward-facing steps in a rectangular channel, especially effects of channel expansion ratio ER upon them. ER treated in the present study was 1.5, 2.0, and 3.0 under a step aspect ratio of 36.0. The Reynolds number Re based on the mean velocity at inlet and the step height was varied from 300 to 1000. The present numerical results for ER=2.0 were found to be in very good agreement with the previous experimental and numerical ones in the present Reynolds number range for both the steady and unsteady flow states. The time averaged reattachment length on the center line increases with a decrease of ER. The flow became unsteady at RE=700, 600, and 500 for ER=1.5, 2.0, and 3.0, respectively, accompanying the remarkable increase of the three-dimensionality of the flow and temperature fields in spite of a very large step aspect ratio of 36.0. The Nusselt number increases in the reattachment flow region, in the neighborhood of the sidewalls, and also in the far downstream depending on both Re and ER.
Forced Convection Heat Transfer and Hydraulic Losses in Graphitic Foam
Authors: Straatman A. G. , Gallego N. C. , Yu Q. , Betchen L. , Thompson B. E.
Published: September 2007

Experiments and computations are presented to quantify the convective heat transfer and the hydraulic loss that is obtained by forcing water through blocks of graphitic foam (GF) heated from one side. Experiments have been conducted in a small-scale water tunnel instrumented to measure the pressure drop and the temperature rise of water passing through the foam and the base temperature and heat flux into the foam block. The experimental data were then used to calibrate a thermal non-equilibrium finite-volume model to facilitate comparisons between GF and aluminum foam. Comparisons of the pressure drop indicate that both normal and compressed aluminum foams are significantly more permeable than GF. Results of the heat transfer indicate that the maximum possible heat dissipation from a given surface is reached using very thin layers of aluminum foam due to the inability of the foam to entrain heat into its internal structure. In contrast, graphitic foam is able to entrain heat deep into the foam structure due to its high extended surface efficiency and thus much more heat can be transferred from a given surface area. The higher extended surface efficiency is mainly due to the combination of moderate porosity and higher solid-phase conductivity.
Dual Solutions in Magnetohydrodynamic Mixed Convection Flow Near a Stagnation-Point on a Vertical Surface
Authors: Ishak A. , Nazar R. , Arifin N. M. , Pop I.
Published: September 2007

The steady magnetohydrodynamic (MHD) mixed convection stagnation-point flow toward a vertical heated surface is investigated in this study. The external velocity impinges normal to the vertical surface and the surface temperature are assumed to vary linearly with the distance from the stagnation point. The governing partial differential equations are transformed into a system of ordinary differential equations, which is then solved numerically by a finite-difference method. The features of the flow and heat transfer characteristics for different values of the governing parameters are analyzed and discussed. Both assisting and opposing flows are considered. It is found that dual solutions also exist for the assisting flow, besides that usually reported in the literature for the opposing flow.
Performance Evaluation of a Compartmented Cooling Coil Using the Monte Carlo Simulation Approach
Authors: Maheswaran Uma , Sekhar S. C.
Published: September 2007

A compartmented cooling coil is a single undivided coil section located in an intermediate point between the upstream and downstream sections of the air handling unit. A thermally insulated metal barrier is provided for the separation of two different air streams that are conditioned through the coil. The coolant flow through the heat exchanger is such that both the air streams encounter each pass of the coolant feed. This paper aims to address the performance of a compartmented coil through the concept of fin efficiency. The compartmented coil geometry involves two distinct sets of air-side characteristics coupled with one set of coolant-side characteristics and it is practically difficult to obtain the values of fin efficiency through empirical measurements alone over a wide range of operating conditions. Hence, the conventional methods of evaluation resort to numerical models for predicting fin performance. The paper questions the validity of certain fundamental assumptions based on which conventional models have been formulated to obtain the local heat transfer coefficient values. A simplified numerical model is formulated and evaluated using a Monte Carlo simulation approach. Performance curves across all ranges of input values are presented and empirical results are used to validate these curves at intermediate values. Results show that air face velocity and surface temperature at a given point on the fin has significant impact on the heat transfer coefficient. It is also shown that for a given fin height of 9.5mm, the assumption of an average heat transfer coefficient as calculated from the LMTD method could vary significantly up to 10% from the predicted results.
Integration of a Quantitative Feedback Theory (QFT)-Based Active Noise Canceller and 3D Audio Processor to Headsets
Authors: Bai Mingsian R. , Lin Jianliang
Published: September 2007

This paper seeks to enhance the quality of spatial sound reproduction by integrating two advanced signal processing technologies, active noise control (ANC) and three-dimensional (3D) audio, to a headset. The ANC module of the headset is designed based on the quantitative feedback theory (QFT), which is a unified theory that emphasizes the use of feedback for achieving the desired system performance tolerances in the face of plant uncertainties and plant disturbances. Performance, stability, and robustness of the closed-loop system have been taken into account in the loop-shaping procedure within a general framework of the QFT. On the other hand, 3D audio processing algorithms including the head-related-transfer-function and the reverberator are realized on the platform of a fixed-point digital signal processor. Listening tests were conducted to evaluate the proposed system in terms of various subjective performance indices. The experimental results revealed that the 3D headset is capable of delivering superior rendering quality of localization and spaciousness, with the aid of the ANC module.
A State-Switched Absorber Used for Vibration Control of Continuous Systems
Authors: Holdhusen Mark H. , Cunefare Kenneth A.
Published: September 2007

A state-switched absorber (SSA) is a device that is capable of switching between discrete stiffnesses; thus, it is able to instantaneously switch between resonance frequencies. The state-switched absorber is essentially a passive vibration absorber between switch events; however, at each switch event the SSA instantly “retunes” its natural frequency and maintains that frequency until the next switch event. This paper considers the optimization of the state-switched absorber applied to a continuous vibrating system and details the experimental validation of these simulation results. A simulated annealing optimization algorithm was utilized to optimize the state-switched absorber. For the most part, the SSA performed only marginally better than a classical tuned vibration absorber (TVA). However, for a select few cases considered, the SSA was able to reduce the kinetic energy of the plate to which it is attached by 12.9dB over that of a classical tuned vibration absorber. The optimal SSA location on a clamped square plate was near the center of the plate for the vast majority of the forcing cases considered. To experimentally validate the simulation, a SSA was fabricated by employing magnetorheological elastomers to achieve a stiffness change. For several two-force component excitations, several tuning configurations of the SSA were applied and the kinetic energy of the system was found and optimized. As with the majority of the optimization cases, the experiments showed the SSA outperforming the TVA by only 2dB. When comparing the observed results to those found via simulation, the simulations accurately predicted the performance of the SSA in the experiments.
Design Methodology for Microelectromechanical Systems. Case Study: Torsional Scanner Mirror
Authors: Meral Faik Can , Basdogan Ipek
Published: September 2007

Future optical microsystems, such as microelectromechanical system (MEMS) scanners and micromirrors, will extend the resolution and sensitivity offered by their predecessors. These systems face the challenge of achieving nanometer precision subjected to various disturbances. Predicting the performance of such systems early in the design process can significantly impact the design cost and also improve the quality of the design. Our approach aims to predict the performance of such systems under various disturbance sources and develop a generalized design approach for MEMS structures. In this study, we used ANSYS for modeling and dynamic analysis of a torsional MEMS scanner mirror. ANSYS modal analysis results, which are eigenvalues (natural frequencies) and eigenvectors (mode shapes), are used to obtain the state-space representation of the mirror. The state-space model of the scanner mirror was reduced using various reduction techniques to eliminate the states that are insignificant for the transfer functions of interest. The results of these techniques were compared to obtain the best approach to obtain a lower order model that still contains all the relevant dynamics of the original model. After the model size is reduced significantly, a disturbance analysis is performed using Lyapunov approach to obtain root-mean-square values of the mirror rotation angle under the effect of a disturbance torque. The magnitude levels of the disturbance torque are obtained using an experimental procedure. The disturbance analysis framework is combined with the sensitivity analysis to determine the critical design parameters for optimizing the system performance.
Mechanical Design of Robotic In Vivo Wheeled Mobility
Authors: Rentschler Mark E. , Farritor Shane M. , Iagnemma Karl D.
Published: September 2007

A new approach to laparoscopic surgery involves placing a robot completely within the patient. These in vivo robots are then able to provide visual feedback and task assistance that would otherwise require additional incisions. Wheeled in vivo robots can provide a mobile platform for cameras, graspers, and other sensory devices that assist in laparoscopy. Development of wheeled in vivo mobile robots was achieved through a design process that included modeling, finite element analysis (FEA), bench top testing, and animal tests. Laboratory testing using a wheel test platform identified a helical wheel design as the best candidate. Finite element simulations were then used to better understand how changing the helical wheel geometric parameters affected drawbar force. Several prototype mobile robots were then developed based on these results. The drawbar forces of these robots were measured in the laboratory to confirm the FEA results. Finally, these robots were successfully tested during animal surgeries.
Design Concept Generation: A Hierarchical Coevolutionary Approach
Authors: Jin Yan , Li Wei
Published: September 2007

As design problems become more complex and design lead time more pressing, designers need effective support tools to expand their design space exploration. In this paper, a hierarchical coevolutionary approach is proposed to support designers by automatically generating design concepts based on the designers’ inputs. The approach adopts a zigzag design process in which function structures and their corresponding solution principles coevolve in parallel across different levels of an abstraction hierarchy. A grammar-based approach is applied to decompose higher-level functions and generate an initial population of function structures. From this initial population, a coevolutionary algorithm is devised to coevolve more function structures and their corresponding solution principles. A case study of designing a mechanical personal transporter is presented to demonstrate the effectiveness and features of the proposed approach.
A Way to Improve the Accuracy of Hobbed Involute Gears
Authors: Radzevich Stephen P.
Published: September 2007

Involute gears are widely used in the design of machines and mechanisms. Performance of gear transmissions, e.g., performance of automobile transmissions, strongly depends upon the accuracy of gears of which the transmission is comprised. The higher the gear accuracy, the higher performance of the gear transmission observed. An increase of accuracy of involute gears reduces vibration of the transmission, and causes lower noise excitation. A significant amount of gears for the needs of the automotive industry is manufactured by hobbing. Reported in this paper is a way to improve the accuracy of hobbed involute gears that requires an appropriate alteration of design parameters of the hob to be applied. The required correction of design parameters of the hob can be computed on the premises of in-depth analysis of kinematic geometry of meshing of the hob and of the work gear, i.e., of design parameters of the hob, as well as an analysis of kinematics of meshing of the gear work and of the hob. An analytical approach for computation of the required alterations in design parameters of the involute hob is reported in the paper. Using commercial software MathCAD/Scientific, numerous computer codes are developed for performing the necessary computations. A numerical example of computation is presented. The reported results of research are ready to put into production.
A Method to Ensure Preference Consistency in Multi-Attribute Selection Decisions
Authors: Kulok Michael , Lewis Kemper
Published: September 2007

A number of approaches for multi-attribute selection decisions exist, each with certain advantages and disadvantages. One method that has recently been developed, called the hypothetical equivalents and inequivalents method (HEIM) supports a decision maker (DM) by implicitly determining the importances a DM places on attributes using a series of simple preference statements. In this and other multi-attribute selection methods, establishing consistent preferences is critical in order for a DM to be confident in his/her decision and its validity. In this paper, a general preference consistency method is developed, which is used to ensure that a consistent preference structure exists for a given DM. The method is demonstrated as part of HEIM, but is generalizable to any cardinal or ordinal preference structure, where the preferences can be over alternatives or attributes. These structures play an important role in making selection decisions in engineering design including selecting design concepts, materials, manufacturing processes, and configurations, among others. The theoretical foundations of the method are developed and the need for consistent preferences is illustrated in the application to a drill selection case study where the decision maker expresses inconsistent preferences.
Performance of Sliders Flying Over Discrete-Track Media
Authors: Li Jianhua , Xu Junguo , Shimizu Yuki
Published: September 2007

A simulation method in which grooves are virtually distributed on the slider air bearing instead of on the grooved medium surface has been developed and used to investigate the performance of sliders flying over the surface of a discrete-track medium. The simulated flying height loss due to a discrete-track medium coincides well with the measured data, whereas the average-estimation method overestimates flying height loss. Among the characteristics of a slider flying over the surface of a discrete-track medium that were studied are the flying attitude, the effect of groove parameters on flying profile, and the flying height losses due to manufacturing variation and altitude. The results indicate that when a slider is flying over the surface of a discrete-track medium, it will have a higher 3σ of flying height, be more sensitive to altitude, and will have a greater flying height loss.
Stiffness and Damping of Thin PFPE Lubricant Bridging Between Magnetic Disk and Diamond Probe Tip
Authors: Mitsuya Yasunaga , Ohshima Yasuji , Zhang Hedong , Aoyama Kei , Kawai Toshiyuki , Fukuzawa Kenji
Published: September 2007

Spring constants and damping coefficients of a thin lubricant bridge of a perfluoropolyether (PFPE) lubricant intervening between a diamond probe tip and a diamond-like carbon (DLC) surface of a magnetic disk are identified through regression analysis of tip damping vibration. PFPE lubricants with functional end groups were used to form a lubricant bridge between the DLC surface and a probe tip with a notably small curvature radius of 0.1μm. The tip was both retracted from and extended toward the disk surface at four different progressive distances to attain varied elongation of the bridge. It was also vibrated at each step to provide damping waveforms. By applying regression analysis to the observed waveforms, the spring constant and the damping coefficient of the lubricant bridge were identified within an elongation range from 50nm to 800nm. Spring constant of the lubricant bridge kb had a negative value varying from −0.15N∕m to −0.1N∕m. The damping value expressed in the form of frequency-multiplied damping cb×ω ranged from 0.02N∕m to 0.06N∕m. Note that both the absolute value of spring constant ∣kb∣ and frequency-multiplied damping cb×ω exhibited U-shaped variation with lubricant bridge elongation; that is, those values decrease with bridge elongation and they begin to increase after reaching the minimum. The variation in the spring constant was found to be in good accordance with the quasi-static stiffness of the lubricant bridge, and variation in the damping coefficient was explained by energy loss arising in the vibrating lubricant bridge.