249 research outputs found
Parametric Study on the Dynamic Heat Storage Capacity of Building Elements
In modern, extensively glazed office buildings, due to high solar and internal loads and increased comfort expectations, air conditioning systems are often used even in moderate and cold climates. Particularly in this case, passive cooling by night-time ventilation seems to offer considerable potential. However, because heat gains and night ventilation periods do not coincide in time, a sufficient amount of thermal mass is needed in the building to store the heat. Assuming a 24 h-period harmonic oscillation of the indoor air temperature within a range of thermal comfort, the analytical solution of one-dimensional heat conduction in a slab with convective boundary condition was applied to quantify the dynamic heat storage capacity of a particular building element. The impact of different parameters, such as slab thickness, material properties and the heat transfer coefficient was investigated, as well as their interrelation. The potential of increasing thermal mass by using phase change materials (PCM) was estimated assuming increased thermal capacity. The results show a significant impact of the heat transfer coefficient on heat storage capacity, especially for thick, thermally heavy elements. The storage capacity of a 100 mm thick concrete slab was found to increase with increasing heat transfer coefficients as high as 30 W/m2K. In contrast the heat storage capacity of a thin gypsum plaster board was found to be constant when the heat transfer coefficient exceeded 3 W/m2K. Additionally, the optimal thickness of an element depended greatly on the heat transfer coefficient. For thin, light elements a significant increase in heat capacity due to the use of PCMs was found to be possible. The present study shows the impact and interrelation of geometrical and physical parameters which appreciably influence the heat storage capacity of building elements. 1
Goos-Haenchen induced vector eigenmodes in a dome cavity
We demonstrate numerically calculated electromagnetic eigenmodes of a 3D dome
cavity resonator that owe their shape and character entirely to the
Goos-Haenchen effect. The V-shaped modes, which have purely TE or TM
polarization, are well described by a 2D billiard map with the Goos-Haenchen
shift included. A phase space plot of this augmented billiard map reveals a
saddle-node bifurcation; the stable periodic orbit that is created in the
bifurcation corresponds to the numerically calculated eigenmode, dictating the
angle of its "V". A transition from a fundamental Gaussian to a TM V mode has
been observed as the cavity is lengthened to become nearly hemispherical.Comment: 4 pages, 4 figure
Field of study and partner choice
© 2021There is strong assortative mating by field of study. To examine to which extent this is due to self selection or to a causal effect of access to specific ”marriage markets”, we use data from participants in admission lotteries of four oversubscribed studies in the Netherlands. For each of the four studies, we find that the winning compliers of an admission lottery are significantly more likely than the losing compliers to have a partner from the lottery study, whereas losing compliers are only marginally more likely to have a partner from the lottery study than would occur under random matching. These results indicate that assortative mating by field of study is largely due to marriage market access and that self selection plays a minor role. JEL-codes: I26, J12, J13
Unified theory for Goos-H\"{a}nchen and Imbert-Fedorov effects
A unified theory is advanced to describe both the lateral Goos-H\"{a}nchen
(GH) effect and the transverse Imbert-Fedorov (IF) effect, through representing
the vector angular spectrum of a 3-dimensional light beam in terms of a 2-form
angular spectrum consisting of its 2 orthogonal polarized components. From this
theory, the quantization characteristics of the GH and IF displacements are
obtained, and the Artmann formula for the GH displacement is derived. It is
found that the eigenstates of the GH displacement are the 2 orthogonal linear
polarizations in this 2-form representation, and the eigenstates of the IF
displacement are the 2 orthogonal circular polarizations. The theoretical
predictions are found to be in agreement with recent experimental results.Comment: 15 pages, 3 figure
Goos-H\"anchen shifts in frustrated total internal reflection studied with wave packet propagation
We have investigated that the Goos-H\"anchen (GH) shifts in frustrated total
internal reflection (FTIR) studied with wave packet propagation. In the
first-order approximation of the transmission coefficient, the GH shift is
exactly the expression given by stationary phase method, thus saturates an
asymptotic constant in two different ways depending on the angle of incidence.
Taking account into the second-order approximation, the GH shift always depends
on the width of the air gap due to the modification of the beam width. It is
further shown that the GH shift with second-order correction increases with
decreasing the beam width at the small incidence angles, while for the large
incidence angles it reveals a strong decrease with decreasing the beam width.
These phenomena offers the better understanding of the tunneling delay time in
FTIR.Comment: 4 pages, 3 figure
Control of Goos-Hanchen shift of a light beam via a coherent driving field
We present a proposal to manipulate the Goos-Hanchen shift of a light beam
via a coherent control field, which is injected into a cavity configuration
containing the two-level atomic medium. It is found that the lateral shifts of
the reflected and transmitted probe beams can be easily controlled by adjusting
the intensity and detuning of the control field. Using this scheme, the lateral
shift at the fixed incident angle can be enhanced (positive or negative) under
the suitable conditions on the control field, without changing the structure of
the cavity.Comment: 12 pages, 5 figure
Goos-Haenchen shift and localization of optical modes in deformed microcavities
Recently, an interesting phenomenon of spatial localization of optical modes
along periodic ray trajectories near avoided resonance crossings has been
observed [J. Wiersig, Phys. Rev. Lett. 97, 253901 (2006)]. For the case of a
microdisk cavity with elliptical cross section we use the Husimi function to
analyse this localization in phase space. Moreover, we present a semiclassical
explanation of this phenomenon in terms of the Goos-Haenchen shift which works
very well even deep in the wave regime. This semiclassical correction to the
ray dynamics modifies the phase space structure such that modes can localize
either on stable islands or along unstable periodic ray trajectories.Comment: 9 pages, 14 figures in reduced qualit
Steering the Ultrafast Opening and Closure Dynamics of a Photochromic Coordination Cage by Guest Molecules
Photochemical studies on supramolecular hosts that can encapsulate small guest molecules commonly focus on three aspects: photoswitching the cage to release or trap the guest, the effect of the confining environment on the guest, and light-induced exciton or charge transfer within the cage structure. Here, we exploit ultrafast spectroscopy to address how the guest alters the photoswitching characteristics of the cage. For this, the impacts of three disparate guest compounds on ring-opening or ring-closure of a dithienylethene (DTE) ligand in a photoswitchable DTE-based coordination cage are juxtaposed. The guest modulates both outcome and timescale of the cage's photodynamics, by an interplay of structural strain, heavy-atom effect, and enhancement of charge-transfer processes exercised by the guest on the photo-excited cage. The approach might prove beneficial for attuning the applicability of photoswitchable nanocontainers and desired guest compounds
Steuerung der ultraschnellen Öffnungs‐ und Schließungsdynamik eines photochromen Koordinationskäfigs durch Gastmoleküle
Photochemische Studien über supramolekulare Wirte, die kleine Gastmoleküle einkapseln können, konzentrieren sich zumeist auf drei Aspekte: Die Photoschaltung des Käfigs, um den Gast freizusetzen oder einzufangen, die Wirkung der Käfigumgebung auf den Gast und die lichtinduzierte Exzitonen- oder Ladungsübertragung innerhalb der Käfigstruktur. Hier nutzen wir ultraschnelle Spektroskopie, um zu untersuchen, wie der Gast die Photoschaltcharakteristik des Käfigs verändert. Zu diesem Zweck werden die Auswirkungen von drei unterschiedlichen Gastmolekülen auf die Ringöffnung oder den Ringschluss eines Dithienylethen (DTE)-Liganden in einem photoschaltbaren Koordinationskäfig auf DTE-Basis einander gegenübergestellt. Der Gast moduliert sowohl das Ergebnis als auch die Zeitskala der Photodynamik des Käfigs durch ein Zusammenspiel von struktureller Wechselwirkung, dem Schweratomeffekt und einer Verstärkung von Ladungstransferprozessen, die der Gast auf den photoangeregten Käfig ausübt. Der Ansatz könnte sich als nützlich erweisen, um die Anwendbarkeit von photoschaltbaren Nanocontainern und gewünschten Gastverbindungen aufeinander abzustimmen
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