1,721,014 research outputs found
Origin of quantum shape effect
Get PDFSize-invariant shape transformation gives rise to the so-called quantum shape
effect in strongly confined systems. While quantum size and shape effects are
often thought to be difficult to distinguish because of their coexistence, it
is actually possible to separate them and focus solely on the shape effect. In
fact, quantum shape effect is a quite different phenomenon from quantum size
effects, as it can have the opposite influence on the physical properties of
nanoscale systems. Here we explore the origin of the quantum shape effect by
theoretically investigating the simplest system that can produce the same
physics: quantum particles in a box separated by a moving partition. The
partition moves quasistatically from one end of the box to the other, allowing
the system to remain in equilibrium with a reservoir throughout the process.
The partition and the boundaries are impenetrable by particles, forming two
effectively interconnected regions. Position of the partition becomes the shape
variable. We investigate quantum shape effect on the thermodynamic properties
of confined particles. In addition, we applied a new analytical model based on
dimensional transitions to accurately predict thermodynamic properties under
the quantum shape effect. A fundamental understanding of quantum shape effects
could pave the way for employing them to engineer physical properties and
design better materials at nanoscale.Comment: 19 pages, 9 figure
<em>On The Upper Limit for Surface Temperature of a Static and Spherical Body</em>
No full textAn upper limit for surface temperature of a static and spherical body in steady state is determined by considering the gravitational temperature drop (GTD). For this aim, abody consisting of black body radiation (BBR) only is considered. Thus, it is assumedthat body has minimum mass and minimum GTD. By solving the Oppenheimer-Volkoff equation, density distribution of self-gravitating thermal photon sphere with infinite radius is obtained. Surface temperature is defined as the temperature at distance of R from centre of this photon sphere. By means of the density-temperature relation of BBR, surface temperature is expressed as a function of central temperature and radius R. Variation of surface temperature with central temperature is examined. It is shown that surface temperature has a maximum for a finite value of central temperature. For this maximum, an analytical expression depending on only the radius is obtained. Since a real static and stable body with finite radius has much more mass and much more GTD than their values considered here, obtained maximum constitutes an upper limit for surface temperature of a real body. This limitation on surface temperature also limits the radiative energy lose from a body. It is shown that this limit for radiative energy lose is a constant independently from body radius and central temperature. Variation of the minimum mass with central temperature is also examined. It is seen that the surface temperature and minimum mass approach some limit values, which are less than their maximums, by making damping oscillations when central temperature goes to infinity.</p
<em>Surface dependence in thermodynamics of ideal gases</em>
No full textThe Casimir-like size effect rises in ideal gases confined in a finite domain due to the wave character of atoms. By considering this effect, thermodynamic properties of an ideal gas confined in spherical and cylindrical geometries are derived and compared with those in rectangular geometry. It is seen that anideal gas exhibits an unavoidable quantum surface free energy and surface over volume ratio becomes a control variable on thermodynamic state functions in microscale. Thermodynamics turns into non-extensive thermodynamics and geometry difference becomes a driving force since the surface over volumeratio depends on the geometry.</p
<em>High Temperature Corrections For The Classical Expressions Of Radiative Losses From A Black-Body</em>
No full textThe contribution from thermally generated electron–positron pairs to the radiativelosses from a black body is considered near the temperature corresponding to the electron’srest mass energy Tc= mec2/k. The correction factors are defined as the ratio of correctedexpressions (which also include the contribution from thermal pairs) to the classical expressions(which include merely photons). The correction factors for energy, free energy, and entropyfluxes have different values about 0.5Tc, while they have the same value at T << Tc and T >> Tc. The Stephan–Boltzmann’s constant becomes temperature dependent due to thecontribution of thermal pairs. According to the classical expressions of radiative losses, the ratioof energy flux to the absolute value of free energy flux is a constant and it is equal to 3. On thecontrary, it is shown that it is a function of temperature about Tc and it has a maximum about0.38Tc. The correction factor for mean energy per emitted thermal particle has also a maximumabout T = 0.42Tc.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Quantum shape oscillations in the thermodynamic properties of confined electrons in core-shell nanostructures
Get PDFQuantum shape effect appears under the size-invariant shape transformations
of strongly confined structures. Such a transformation distinctively influences
the thermodynamic properties of confined particles. Due to their characteristic
geometry, core-shell nanostructures are good candidates for quantum shape
effects to be observed. Here we investigate the thermodynamic properties of
non-interacting degenerate electrons confined in core-shell nanowires
consisting of an insulating core and a GaAs semiconducting shell. We derive the
expressions of shape-dependent thermodynamic quantities and show the existence
of a new type of quantum oscillations due to shape dependence, in chemical
potential, internal energy, entropy and specific heat of confined electrons. We
provide physical understanding of our results by invoking the quantum boundary
layer concept and evaluating the distributions of quantized energy levels on
Fermi function and in state space. Besides the density, temperature and size,
the shape per se also becomes a control parameter on the Fermi energy of
confined electrons, which provides a new mechanism for fine tuning the Fermi
level and changing the polarity of semiconductors.Comment: 12 pages, 6 figure
Fractional integral representation in statistical thermodynamics of confined systems
No full textConfined systems are usually treated as integer dimensional systems, like two dimensional (2D), 1D, and 0D, by considering extreme confinement conditions in one or more directions. This approach costs piecewiserepresentations, some limitations in confinement interval, and the deviations from the true behaviors,especially when the confinement is neither strong nor weak. In this study, fractional integral representation(FIR) is proposed as a methodology to calculate the infinite summations in statistical thermodynamics forany dimension and confinement values. FIR directly incorporates the dimension as a control variable intocalculation procedures and allows us to get solutions valid for the whole confinement and dimension scales,including the fractional ones. We define the dimension of a summation and used it in the proposed FIRto calculate the partition function. The first and the higher-order FIR are introduced and high accuracyresults are achieved. FIR is then extended for a generalized function to calculate thermodynamic propertiesdirectly from their fundamental expressions based on infinite sums. By using the proposed FIR approach, thethermodynamic properties of a noninteracting Maxwell-Boltzmann gas confined in an elongated rectangulardomain are determined. The excess quantities induced by confinement are examined for different confinementscenarios. FIR successfully predicts the true behavior of thermodynamic properties for the whole range ofconfinement and dimension scales. Defining and controlling the dimension allows designing new types ofthermodynamic cycles. Besides the infinite-well potential for the confinement of particles with quadratic andlinear dispersion relations, quadratic and quartic confining potentials are also considered to show the successof FIR. The proposed method not only incorporates the dimension into the calculation procedures butalso constitutes an application of fractional calculus in statistical thermodynamics. FIR has many potentialapplications especially for Bose-Einstein condensation phenomenon which inherently contains dimensionaltransitions
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
<em>Experimental and computational investigation of multi U-tube boreholes</em>
No full textIn ground source heat pump (GSHP) applications, borehole drilling cost constitutes an important part ofthe investment cost and it can be reduced by improving borehole performance. In vertical GSHP applications,usually double-U tube configurations are used to improve the heat transfer rate per unit length of aborehole, (unit HTR value). To determine the optimal number of U-tubes which maximizes the commercialand engineering benefits of multi U-tube applications, cost and performance analyses of multi U-tubeboreholes are crucial. In this study, a triple U-tube is used in a borehole of 50 m depth. Time variation ofunit HTR value of the borehole is experimentally measured when single, double and triple U-tubes are inoperation separately. Furthermore a computational model is calibrated by fitting the computationalresults to the experimental ones, and effects of using four and five U-tubes in a borehole are computationallyinvestigated. The relations between number of U tubes and time variation of unit HTR value ofa borehole as well as investment cost are analyzed. Long term borehole performance predictions aremade and compared for multi U-tube applications. Both experimental and computational results showedthat performance improvements are remarkable for 2U-tube and 3U-tube configurations while it isnearly insignificant for 4U and 5U ones. If the investment cost per thermal power is considered, 2U-tubeconfiguration is the optimal one if the prices of polyethylene pipes are relatively high, like in Turkey.When the cost of pipes decreases, then 3U-tube or even 4U–tube configuration can be the cheapestsolution.</p
- …
