Passive Space Research Articles

Active Acoustic Systems for the Control of Room Acoustics

The acoustic design of auditoria involves the specification of the room geometry and boundary properties, and any additional acoustic elements such as reflectors or diffusers, to usefully direct sound to produce a desired subjective experience, quantified by measurable acoustic parameters. This design must take into account the reflection of sound within the stage area, the early reflections from the stage to the audience and the reverberant response of the room. The sound produced by the audience can also be an important consideration. Active acoustic systems provide an alternative approach to controlling subjective experience. They use microphones, electronic processors and loudspeakers to create reflections and reverberation in addition to those produced by the naturally-occurring sound field. The acoustic properties can be changed instantly, and the enhanced acoustic properties of the auditorium can typically be varied over a wider range than can be produced by variable passive techniques. The design of active acoustics follows that of passive approaches, but rather than the physical arrangement of the room surfaces, it commences with an existing passive space with some minimum acoustic condition, and requires the arrangement of microphones to detect relevant sound and the choice of processors and loudspeaker positions to direct it usefully back into the room to produce a desired set of acoustic parameters. While active systems have historically been developed with the goal of enhancing either the stage or audience sound, they must generally provide the same control of sound as passive acoustic design. This paper discusses the principles of active acoustic systems and how they are used to achieve the required range of control. A survey of current commercial systems is given and some implications for the future of live performance are explored.

Conflicts in science the classroom: Documentation and management through phenomenological methodology

The study investigated the nature of conflicts that are generated in the science classroom. Twenty video-recorded lessons taught by 10 randomly selected pre-service science teachers in teaching practice in a few Nigerian secondary schools were analyzed. Beside the expected goal attainment of the lessons a number of negative conflicts were documented. The analysis of the responses to the questionnaire administered to further sample of 220 serving science teachers presented in charts not only confirmed the occurrences of these negative instances but attributed them to students’ poor home background and upbringing, They attributed students’ success and good performance to teachers’ dedication and employment of good teaching methods, strategies and approaches. The subjects played down the contributions from government and parents. A number of remediation strategies meant to carry all students along in teaching-learning situation were made. These include adequately equipped laboratories, provision of appropriate incentive environment for teachers, retraining and counseling. The author sees these useful but predictable findings as part of a customary teacher’s narrative and rhetoric. For that reason, this study sought to adopt a phenomenological methodology by reconstituting these surface experiences afresh and at deep level perceptions. One suggestion is science excursions for students who for one reason or the other are prone to causing these conflicts. Such excursions can take the students to a science museum or science exhibition that offers hands-on involvement and can help change their attitudes towards learning science inside the more passive space of the classroom. Keywords: Science classroom, nature of conflicts, classroom management, phenomenological methodology.

(R)Evolution of Indexing Methods - Why Diversification Was Forgotten?

In the modern era of investing, diversification has become the cornerstone of most asset managers’ investment philosophy. Within the equity space, the primary focus of most institutional investors has been to diversify their active equity managers – combining equity funds exhibiting uncorrelated return sources such as value, growth, momentum and size – in order to smooth the relative return generation. Remarkably, the ingrained virtues of diversification have hardly made their way through to the passive equity investment space. Market capitalisation-weighted indexing still represents the vast majority of assets invested in passive equity strategies. However, over the past few years, a paradigm shift has started to occur, with a new breed of passive indexing approaches entering the passive equity space. Investors are now starting to evaluate and invest into new passive indexing approaches, looking to diversify among their passive managers as well. The objective of this white paper is to scrutinise these new alternatives to traditional passive investing.

Energy Performance of a Building-Integrated Dual-Function Solar Collector in Passive Space Heating Mode

The building-integrated dual-function solar collector has two independent operating modes: passive space heating mode in cold days, and solar water heating mode during hot days such as the summer. The novel system avoids summer overheating in hot climate and water-freezing in cold climate, meanwhile remains low operating cost as a passive solar heating system. In this study, the energy performance of the novel system in passive space heating mode was studied by experiment and numerical simulation. The experimental and numerical results show that the system performed a high ability in utilizing solar energy for building when working in passive space heating mode and the value of the transient operating efficiency generally kept as a constant.

Stearic acid/silica fume composite as form-stable phase change material for thermal energy storage

The aim of this research is to prepare a novel form-stable composite phase change material (PCM) for the latent heat thermal energy storage (LHTES) in buildings, passive solar space heating by impregnating of stearic acid (SA) into silica fume (SF) matrix through the technique of solution impregnation. The structure, thermal properties, thermal reliability, thermal conductivity and heat storage or release performance of the composite PCM were determined by scanning electron microscope (SEM), Fourier transformation infrared (FTIR), differential scanning calorimetry (DSC) and thermal cycling test analysis technique. The results show that the form-stable composite PCM has the optimal effect, preventing the leakage of SA from the composite, emerges when the SA and SF mass ratio is 1:0.9. The SA loaded on the matrix surface by physical attraction with the mass ratio of 47% during the preparation process. The latent heat of the composite PCM is measured as 82.53 J/g for the melting process and 84.47 J/g for the freezing process, respectively, which indicate the heat storage ability of composite is connected with the mass ratio of SA in composite. The results of DSC, FTIR and thermal cycling test are all show that the thermal reliability of the composite PCM has an imperceptible change. The increase of thermal conductivity was also confirmed by comparing the melting time, freezing time and phase change time of the composite with that of SA. All of the conclusions indicate that the composite has a better thermal conductivity and good thermal and chemical stability.

Modelling and validation of a building-integrated dual-function solar collector

A novel building-integrated solar thermal system known as building-integrated dual-function solar collector is proposed. The system has two independent operating modes: passive space heating mode and water heating mode, and it uses the following criteria to select the operating mode that during cold days such as winter days it works in passive space heating mode, but in warm seasons such as summer it works in the water heating mode. A testing system was established, and it performed in thermosiphon water heating mode for water heating. Two dynamic numerical models were, respectively, presented for the two operating modes of the testing system. The experimental data on the testing system were used to validate the two models. The results show that the numerical model for the system in the thermosiphon water heating mode can give a fairly good prediction and the model for the system in the space heating mode also gives a good prediction.

Impedance and complex power of radiating elements under electromagnetic source transformation

AbstractTransformation optics is a methodology that has proven useful in the design of complex media used to alter and control electromagnetic waves in either passive space or regions that contain source distributions. Recently it has been shown that the application of source transformations can reshape field radiation patterns corresponding to arbitrarily shaped sources. In the accompanying numerical confirmations, the effect of source transformations on fundamental quantities that are critical to the design and evaluation of antenna based systems‐‐such as complex power and impedance, remain unexplored. In this paper, we present results of theoretical analysis as well as full wave finite element simulations, proving that the complex power and impedance associated with an electromagnetic source are not changed by source transformation methods. These results open the door to the application of source transformations for the design of practical antenna based systems, such as conformal and phased array antenna design. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26077

Eicosane/Polycarbonate Composite as Form-Stable Phase Change Materials for Latent Heat Thermal Energy Storage

The aim of this research is to prepare of a novel form-stable composite phase change materials (PCMs) for the latent heat thermal energy storage (LHTES) in buildings, passive solar space heating or functional fluid by incorporation of eicosane within Polycarbonate (PC) through solution casting technique. The composite PCMs was characterized using scanning electron microscope (SEM) and fourier transformation infrared (FTIR) analysis technique. The results show that the form-stable blends was formed and the maximum encapsulated proportion of eicosane in the composite was 50 wt% without melted PCMs seepage from the composite. In the shape stabilized PCMs, the polymer acts as the supporting material to form the there dimensional network structure and the eicosane acts as a PCMs and disperses in the three-dimensional network structure. Thermal properties, thermal reliability and heat storage or release performance of the composite PCMs were determined by differential scanning calorimetry (DSC), FTIR and thermal cycling test analysis. The melting and freezing temperatures and the latent heats of the composite PCM were measured as 36.2°C-40°C and 62.2 J/g - 63.1 J/g, respectively. The results of DSC, FTIR and thermal cycling test are all show that the thermal reliability of the composite PCMs has an imperceptible change. This conclusion indicates that the blends have a good thermal and chemical stability.

Stearic acid/polymethylmethacrylate composite as form-stable phase change materials for latent heat thermal energy storage

The aim of this research is to prepare of a novel form-stable composite phase change material (PCM) for the latent heat thermal energy storage (LHTES) in buildings, passive solar space heating or functional fluid by entrapping of SA into PMMA cell through ultraviolet curing dispersion polymerization. The composite PCM was characterized using scanning electron microscope (SEM) and Fourier transformation infrared (FT-IR) analysis technique. The results show that the form-stable microencapsulated PCM with core/shell structure was formed and the maximum encapsulated proportion of SA in the composite was 51.8 wt.% without melted PCM seepage from the composite. In the shape stabilized microencapsulated PCM, the polymer acts as supporting material to form the microcapsule cell preventing the leakage of PCM from the composite and the SA acts as a PCM encapsulated in the cell of PMMA resin. The oxygen atom of carbonyl group of skeleton is interacted with the hydrogen atom of hydroxyl group of SA. Thermal properties, thermal reliability and heat storage/release performance of the composite PCM were determined by differential scanning calorimetry (DSC), FT-IR and thermal cycling test analysis. The melting and freezing temperatures and the latent heats of the composite PCM were measured as 60.4 °C, 50.6 °C and 92.1 J/g, 95.9 J/g, respectively. The results of DSC, FT-IR and thermal cycling test are all show that the thermal reliability of the composite PCM has an imperceptible change. This conclusion indicates that the composite has a good thermal and chemical stability.

Forward Dynamics of the 6-PUS Parallel Manipulator Based on the Force Coupling and Geometry Constraint of the Passive Joints

This paper presents a simplified approach for the forward dynamics of the 6-PUS parallel manipulator. In the proposed method, the parallel manipulator is divided into the limb parts and the platform part at the passive spherical joints. For both parts, the equivalent dynamic equations related to the passive joints are obtained based on the transformation principles of dynamics between different spaces. Then, in acceleration level, the dynamic model for both parts can be rewritten in the form of linear equations on the generalized constraint forces and the linear accelerations of the passive joints on the condition that the state (position and velocity) of the manipulator is specified. According to the force coupling and geometry constraint of passive joints, the closed form solution for the generalized constraint forces can be derived readily from the linear equations combined by the separated parts. In the level of position and velocity, task variables of the manipulator, namely the position and orientation of the moving platform, are chosen as the system's generalized coordinates, which results in the utilization of the inverse kinematics for the state transformation between the workspace and the passive joints space. Consequently, by virtue of the obtained constraint forces, the dynamics of the manipulator can be replaced by a single free rigid body (the platform) with specified external forces provided by the environment through the end-effector and the limbs through the passive spherical joints, respectively. At last, some numerical results are provided and compared to validate the correctness and effectiveness of the proposed approach.

Thermal characteristics of a building-integrated dual-function solar collector in water heating mode with natural circulation

As a modified building-integrated solar thermal system, building-integrated dual-function solar collector here proposed is able to provide passive space heating in cold winter, and water heating in warm seasons. In this study, evaluations were made on this modified collector system for the warm period operation under the water heating mode with natural circulation of flow. A dynamic numerical model has been developed and validated by experimental data. Based on practical air-conditioned room design conditions, numerical analysis was performed to study the water heating performance, as well as to compare the solar transmission through building facade in different seasons with or without its presence. The results show that when working in the water heating mode, the system performs well in providing services hot water in the warm seasons without bringing in summer overheating problem.

Effect of a dual-function solar collector integrated with building on the cooling load of building in summer

As a building integrated solar thermal system, the dual-function solar collector integrated with building works for passive space heating in cold winter season, and for water heating in warm seasons. In this paper, the study is made on the dual-function solar collector integrated with building when it works in water heating mode with natural circulation. The coupled model of the collector and building’s environment is established and validated. A numerical simulation is achieved to show the thermal effect of the novel system on the building in summer. By comparing with the cooling loads of the rooms with or without the novel collector in summer, the results show that when in summer, the novel solar system is available for serving hot water, and it does not have the summer overheating problem, and can even improve the thermal environment of its building slightly.

Developments for vegetation fluorescence retrieval from spaceborne high‐resolution spectrometry in the O2‐A and O2‐B absorption bands

Solar‐induced chlorophyll fluorescence is a weak electromagnetic signal emitted in the red and far‐red spectral regions by vegetation chlorophyll under excitation by solar radiation. Chlorophyll fluorescence has been demonstrated to be a close proxy to vegetation physiological functioning. The basis for fluorescence retrieval from passive space measurements is the exploitation of the O2‐A and O2‐B atmospheric absorption features to isolate the fluorescence signal from the solar radiation reflected by the surface and the atmosphere. High spectral resolution measurements and a precise modeling of the atmospheric radiative transfer in the visible and near‐infrared regions are mandatory. Recent developments for fluorescence retrieval from passive high spectral resolution spaceborne measurements are presented in this work, which has been performed in preparation of the FLuorescence EXplorer (FLEX) mission, which is currently under development by the European Space Agency. A large data set of FLEX‐like measurements has been simulated for the purpose of methodology development and testing. Issues related to vegetation chlorophyll fluorescence retrieval from space, a description of the proposed methodology, initial results from simulated test cases, and general guidelines for the specification of fluorescence retrieval instruments are presented and discussed in this work.

Efficiency of self-ligating vs conventionally ligated brackets during initial alignment

The aim of this study was to compare the efficiency of self-ligating (SL) and conventionally ligated (CL) brackets during the first 20 weeks of extraction treatment. Study models of 50 consecutive patients who had premolar extractions in the maxillary and/or mandibular arch, 0.022 x 0.028-in slot brackets, and similar archwire sequences were examined. Forty-four arches received SL Damon 3MX brackets (Ormco, Glendora, Calif), and 40 arches received either CL Victory Series (3M Unitek, Monrovia, Calif) or Mini-Diamond (Ormco) brackets. The models were evaluated for anterior arch alignment, extraction spaces, and arch dimensions at pretreatment (T0), 10 weeks (T1), and 20 weeks (T2). There were no significant differences between the SL and CL groups at 20 weeks in irregularity scores (mandibular arch, P = 0.54; maxillary arch, P = 0.81). There were no significant differences in passive extraction space closures between the SL and CL groups (mandibular arch, T0-T2, P = 0.85; maxillary arch, T0-T2, P = 0.33). Mandibular intercanine widths increased from T0 to T2: 1.96 and 2.86 mm in the SL and CL groups, respectively. This was not significant between the groups (P = 0.31). Logistic regression did not show a difference between the SL and CL bracket groups. SL brackets were no more efficient than CL brackets in anterior alignment or passive extraction space closure during the first 20 weeks of treatment. Ligation technique is only one of many factors that can influence the efficiency of treatment. Similar changes in arch dimensions occurred, irrespective of bracket type, that might be attributed to the archform of the archwires.

Editor's Comment and Q&A: Efficiency of self-ligating vs conventionally ligated brackets during initial alignment

Introduction The aim of this study was to compare the efficiency of self-ligating (SL) and conventionally ligated (CL) brackets during the first 20 weeks of extraction treatment. Methods Study models of 50 consecutive patients who had premolar extractions in the maxillary or mandibular arch, 0.022 × 0.028-in slot brackets, and similar archwire sequences were examined. Forty-four arches received SL Damon 3MX brackets (Ormco, Glendora, Calif), and 40 arches received either CL Victory Series (3M Unitek, Monrovia, Calif) or Mini-Diamond (Ormco) brackets. The models were evaluated for anterior arch alignment, extraction spaces, and arch dimensions at pretreatment (T0), 10 weeks (T1), and 20 weeks (T2). Results There were no significant differences between the SL and CL groups at 20 weeks in irregularity scores (mandibular arch, P = 0.54; maxillary arch, P = 0.81). There were no significant differences in passive extraction space closures between the SL and CL groups (mandibular arch, T0-T2, P = 0.85; maxillary arch, T0-T2, P = 0.33). Mandibular intercanine widths increased from T0 to T2: 1.96 and 2.86 mm in the SL and CL groups, respectively. This was not significant between the groups (P = 0.31). Logistic regression did not show a difference between the SL and CL bracket groups. Conclusions SL brackets were no more efficient than CL brackets in anterior alignment or passive extraction space closure during the first 20 weeks of treatment. Ligation technique is only one of many factors that can influence the efficiency of treatment. Similar changes in arch dimensions occurred, irrespective of bracket type, that might be attributed to the archform of the archwires.

A numerical and experimental study of a dual-function solar collector integrated with building in passive space heating mode

A newly designed solar collector named dual-function solar collector is proposed. The dual-function solar collector integrated with building can perform in two different modes: working as a passive space heating collector in cold sunny days such as in winter, or working as a facade water heating collector in hot days such as in summer. An experimental study has been carried out to investigate the performance of the novel system in space heating mode, whilst, the dynamic numerical model has been established and validated. The experimental and numerical results show that during the period of the measurement from 9:00 to 17:00, the mean indoor temperature was up to 24.7°C while the mean ambient temperature was only 4.8°C, and a temperature stratification was present in the room. Moreover, a numerical study on the effect of optical property of coatings has been carried out.

Puff-wave transition in an inhomogeneous model for calcium signals

In many cell types, calcium ion channels on the endoplasmic reticulum membrane occur in a clustered distribution. The channels generate either localized puffs, each comprising channels of only one cluster, or global calcium waves. In this work we model the calcium system as a two-dimensional lattice of active elements distributed regularly in an otherwise passive space. We address an important feature of the puff-wave transition, which is the difference in lifetime of puffs at a few hundred milliseconds and long-lived global waves with periods of several seconds. We show that such a lifetime difference between puffs and waves can be understood with strongly reduced ordinary differential equations modified by a time-scale factor that takes into account the coupling strength of active and passive regions determined by the Ca2+ diffusion coefficient. Furthermore, we show that the point model can also describe very well the dependence of Ca2+ oscillation characteristics on the cluster-cluster distance in the case of large diffusivity.

Ionization behavior of deep level donors in passive film formed on surface of stainless steel in 5% salt solution

Deep level donor's ionization behavior of passive film formed on the surface of stainless steel was investigated by Mott-Schottky plots. It is indicated that transformation process of deep level donors' ionization behavior of passive film on surface of stainless steel can be divided into 4 stages with rising immersion time. At the initial immersion stage (10 min), Fe(Ⅱ) located in the octahedral sites of the unit cell is not ionized and the deep level does not appear in Mott-Schottky plots. At the second stage (9−38 h), Fe(Ⅱ) located in the octahedral sites starts to be ionized, which results in deep level donors' generation and density of deep level donors almost is constant with augmenting immersion time but the thickness of space charge layer is more and more thicker with rising immersion time. At the third stage (48 h−12 d), density of deep level donors rises with increasing immersion time and the thickness of passive films space charge layer decreases. At last stage (above 23 d), both the space charge layer's thickness and density of deep level donors are no longer changed with increasing immersion time. In the overall immersion stage, the shallow level donors' density is invariable all the time. The mechanism of deep level donor's ionization can be the generation of metal vacancies, which results in crystal lattice's aberration and the aberration energy urges the ionization of Fe(Ⅱ) in octahedral sites.

125666 FORWARD DYNAMICS OF THE 6-PUS PARALLEL MANIPULATOR BASED ON THE FORCE COUPLING AND GEOMETRY CONSTRAINT OF THE PASSIVE JOINTS(Robotics and Mechatronics)

This paper presents a simplified approach for the forward dynamics analysis of the 6-P__-US parallel manipulator, as shown in figure.1, based on the force coupling and geometry constraint of the passive spherical joints. In the proposed method, the parallel manipulator is divided, at the passive joints, into the limbs parts and the platform part. And for both kinds of parts, the equivalent dynamic equations relating to the decomposing joints are obtained based on the transformation principles of dynamic equations between different spaces. Then, in the acceleration level, the dynamic models for both parts can be rewritten in the form of linear equations on the generalized constraint forces and the accelerations of the passive joints on the condition that the state (position and velocity) of the manipulator is specified. Thus, according to the force coupling and geometry constraints of the passive joints, the closed form solution for the generalized constraint forces can be derived readily from the linear equations system combined by the separated parts. Additionally, in the position/velocity level, the task space variables of the manipulator (the position and orientation of the platform) are chosen as the system generalized coordinates, which only results in the utilization of the inverse kinematics for the state transformation between the workspace and the passive joints space. Hence, by virtue of the constraint forces obtained from the above linear equations, the dynamic model of the parallel manipulator can be replaced by a single free rigid body (the platform) with specified external applied forces, provided by the environment through the end-effector and the limbs through the passive spherical joints, respectively. In the end, some numerical results are provided and compared to validate the correctness and effectiveness of the proposed approach.

All-optical switching between quantum dot nanoarrays

An all-optical switching device is proposed, based on a sandwich structure comprising two-dimensional square-lattice nanoarrays of donor and acceptor quantum dots. The system operates on Förster energy transfer between the dark states of the individual nanoparticles, normally precluded by selection rules. On application of an off-resonant laser beam, a nonlinear mechanism activates transfer between spatially correlated quantum dots across an optically passive spacer layer, signifying an active switching action with parallel processing capability. In this report, electrodynamic theory is employed to analyse the system and to evaluate its energy transfer fidelity. The results of model calculations are presented in graphical form.