25,355 research outputs found

    Low-cost fabrication of printed electronics devices through continuous wave laser-induced forward transfer

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    Laser induced forward transfer (LIFT) is a direct-writing technique that allows printing inks from a liquid film in a similar way to inkjet printing but with fewer limitations concerning ink viscosity and loading particle size. In this work we prove that liquid inks can be printed through LIFT by using continuous wave (CW) instead of pulsed lasers, which allows a substantial reduction in the cost of the printing system. Through the fabrication of a functional circuit on both rigid and flexible substrates (plastic and paper) we provide a proof-of-concept that demonstrates the versatility of the technique for printed electronics applications

    Certified high-efficiency "large-area" perovskite solar cells module for Fresnel lens-based concentrated photovoltaic

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    This is the author accepted manuscript. The final version is available on open access from Cell Press via the DOI in this recordData availability: All data generated or analysed during this study are included in the Supplementary Information article and its data source. Source data are provided in this paper. All data reported in this paper will be shared by the lead contact upon request.The future of energy generation is well in tune with the critical needs of the global economy, leading to more green innovations and emissions-abatement technologies. Introducing concentrated photovoltaic (CPV) is one of the most promising technologies owing to its high photo-conversion efficiency (PCE). While most researchers use silicon and cadmium telluride for CPV, we investigate the potential in nascent technologies, such as perovskite solar cell (PSC). This work constitutes a preliminary investigation into a ‘large-area’ PSC module under a Fresnel lens (FL) with a ‘refractive optical concentrator-silicon-on-glass’ base to minimise the PV performance and scalability trade-off concerning the PSCs. The FL-PSC system measured the solar current-voltage characteristics in variable lens-to-cell distances and illuminations. A systematic study of the PSC module temperature was monitored using the COMSOL transient heat transfer mechanism. The FL-based technique for ‘large-area’ PSC architecture is an unfolded technology that further facilitates the potential for commercialisation.Engineering and Physical Sciences Research Council (EPSRC)Valais Energy Demonstrators FundEuropean Union Horizon 2020Deputyship for Research & Innovation, Ministry of Education, Saudi Arabi

    Quantum dots based superluminescent diodes and photonic crystal surface emitting lasers

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    This thesis reports the design, fabrication, and electrical and optical characterisations of GaAs-based quantum dot (QD) photonic devices, specifically focusing on superluminescent diodes (SLDs) and photonic crystal surface-emitting lasers (PCSELs). The integration of QD active regions in these devices is advantageous due to their characteristics such as temperature insensitivity, feedback insensitivity, and ability to utilise the ground state (GS) and excited state (ES) of the dots. In an initial study concerning the fabrication of QD-SLDs, the influence of ridge waveguide etch depth on the electrical and optical properties of the devices are investigated. It is shown that the output power and modal gain from shallow etched ridge waveguide is higher than those of deep etched waveguides. Subsequently, the thermal performance of the devices is analysed. With increased temperature over 170 ºC, the spectral bandwidth is dramatically increased by thermally excited carrier transition in excited states of the dots. Following this, an investigation of a high dot density hybrid quantum well/ quantum dot (QW/QD) active structure for broadband, high-modal gain SLDs is presented. The influence of the number of QD layers on the modal gain of hybrid QW/QD structures is analysed. It is shown that higher number of dot layer provides higher modal gain value, however, there is lack of emission from QW due to the requirement of large number of carriers to saturate the QD. Additionally, a comparison is made between “unchirped QD” and “ chirped QD” of hybrid QW/QD structure in terms of modal gain and spectral bandwidth. It is showed that “chirped” of the QD can improve the “flatness” of the spectral bandwidth. Lastly, the use of self-assembled InAs QD as the active material in epitaxially regrown GaAs-based PCSELs is explored for the first time. Initially, it is shown that both GS and ES lasing can be achieved for QD-PCSELs by changing the grating period of the photonic crystal (PC). The careful design of these grating periods allows lasing from neighbouring devices at GS ( ~1230 nm) and ES (~1140 nm), 90 nm apart in wavelength. Following this, the effect of device area, PC etch depth, PC atom shape (circle or triangle or orientation) on lasing performance is presented. It is shown that lower threshold current density and higher slope efficiencies is achieved with increasing the device size. The deeper PC height device has higher output power due to more suitable height and minimal distance to active region. The triangular atom shape has slightly higher slope efficiency compared to triangular atom shape which is attributed to breaking in-plane symmetry and increase out-of-plane emission

    Correspondence between field theory in Rindler frame and thermofield-double formalism

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    Considering two accelerated observers with same acceleration in two timelike wedges of Rindler frame we calculate all the thermal Feynmann propagators for a real scalar field with respect to the Minkowski vacuum. Only the same wedge correlators are symmetric in exchange of thermal bath and Unruh thermal bath. Interestingly, they contains a cross term which is a collective effects of acceleration and thermal nature of field. Partucularly the zero temperature description corresponds to usual thermofield double formalism. However, unlike in later formulation, the two fields are now parts of the original system. Moreover it bears the features of a spacial case of closed time formalism where the Keldysh contour is along the increasing Rindler time in the respective Rindler wedges through a specific complex time intra-connector. Hence Rindler frame field theory seems to be a viable candidate to deal thermal theory of fields and may illuminate the search for a bridge between the usual existing formalims.Comment: Latex, 12 pages, 2 figures

    James Webb Space Telescope: data, problems, and resolution

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    It is argued that the data presented by Hubble Space Telescope and James Webb Space Telescope, that seem to be at odds with the canonical big bang cosmology, find simple explanation if galaxy formation is seeded by massive primordial black holes (PBH), as anticipated in 1993 (A. Dolgov and J. Silk, later DS). The statement that the galaxy formation might be seeded by PBH is now rediscovered in several works. The predicted by DS log-normal mass spectrum of PBHs very well agrees with astronomical data. Abundant BH population of the Galaxy with masses of the order of tens solar masses is predicted. Extended mass spectrum of PBH together with their possible clustering allows them to make 100\% contribution into the cosmological dark matter. Another prediction of DS mechanism on noticeable amount of antimatter in the Milky Way also seems to be confirmed by the data.Comment: 23 pages, 10 figures, plenary talk at Plenary talk presented at 36th Rencontres de Physique de la Vall{\'e}e d'Aoste on Results and Perspectives in Particle Physics, extended and update

    Entanglement Islands from Hilbert Space Reduction

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    In this paper we try to understand the \textit{Island formula} from a purely quantum information perspective. We propose that the island phase is a property of the quantum state and the Hilbert space where the state is embedded in. More explicitly we show that, in a quantum system when the state of a subset is totally encoded in the state of another subset, the Hilbert space of the system will reduce, and the way we compute the reduced density matrix and related entropy quantities will also change essentially. Such reductions of the Hilbert space result in a new island formula in quantum systems, which we conjecture to be the same island formula in gravity recently proposed to rescue the unitarity in the process of black hole evaporation. In this context, we give a simple resolution to the Mathur/AMPS paradox. Furthermore, we propose a non-gravitational field theory configuration where entanglement islands emerge, give a description for the entanglement structure of the island phase and propose how to realize the island phase in the lab.Comment: 28pages. Comments are very welcome; V2 references updated, minor revision; V3, footnote 5 adde

    New anisotropic star solutions in mimetic gravity

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    We extract new classes of anisotropic solutions in the framework of mimetic gravity, by applying the Tolman-Finch-Skea metric and a specific anisotropy not directly depending on it, and by matching smoothly the interior anisotropic solution to the Schwarzschild exterior one. Then, in order to provide a transparent picture we use the data from the 4U 1608-52 pulsar. We study the profile of the energy density, as well as the radial and tangential pressures, and we show that they are all positive and decrease towards the center of the star. Furthermore, we investigate the anisotropy parameter and the anisotropic force, that are both increasing functions of the radius, which implies that the latter is repulsive. Additionally, by examining the radial and tangential equation-of-state parameters, we show that they are monotonically increasing, not corresponding to exotic matter. Concerning the metric potentials we find that they have no singularity, either at the center of the star or at the boundary. Furthermore, we verify that all energy conditions are satisfied, we show that the radial and tangential sound speed squares are positive and sub-luminal, and we find that the surface redshift satisfies the theoretical requirement. Finally, in order to investigate the stability we apply the Tolman-Oppenheimer-Volkoff equation, we perform the adiabatic index analysis, and we examine the static case, showing that in all cases the star is stable.Comment: 20 pages 10 figures, will appear in EPJ

    A direct-laser-written heart-on-a-chip platform for generation and stimulation of engineered heart tissues

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    In this dissertation, we first develop a versatile microfluidic heart-on-a-chip model to generate 3D-engineered human cardiac microtissues in highly-controlled microenvironments. The platform, which is enabled by direct laser writing (DLW), has tailor-made attachment sites for cardiac microtissues and comes with integrated strain actuators and force sensors. Application of external pressure waves to the platform results in controllable time-dependent forces on the microtissues. Conversely, oscillatory forces generated by the microtissues are transduced into measurable electrical outputs. After characterization of the responsivity of the transducers, we demonstrate the capabilities of this platform by studying the response of cardiac microtissues to prescribed mechanical loading and pacing. Next, we tune the geometry and mechanical properties of the platform to enable parametric studies on engineered heart tissues. We explore two geometries: a rectangular seeding well with two attachment sites, and a stadium-like seeding well with six attachment sites. The attachment sites are placed symmetrically in the longitudinal direction. The former geometry promotes uniaxial contraction of the tissues; the latter additionally induces diagonal fiber alignment. We systematically increase the length for both configurations and observe a positive correlation between fiber alignment at the center of the microtissues and tissue length. However, progressive thinning and “necking” is also observed, leading to the failure of longer tissues over time. We use the DLW technique to improve the platform, softening the mechanical environment and optimizing the attachment sites for generation of stable microtissues at each length and geometry. Furthermore, electrical pacing is incorporated into the platform to evaluate the functional dynamics of stable microtissues over the entire range of physiological heart rates. Here, we typically observe a decrease in active force and contraction duration as a function of frequency. Lastly, we use a more traditional ?TUG platform to demonstrate the effects of subthreshold electrical pacing on the rhythm of the spontaneously contracting cardiac microtissues. Here, we observe periodic M:N patterns, in which there are ? cycles of stimulation for every ? tissue contractions. Using electric field amplitude, pacing frequency, and homeostatic beating frequencies of the tissues, we provide an empirical map for predicting the emergence of these rhythms

    The temporality of rhetoric: the spatialization of time in modern criticism

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    Every conception of criticism conceals a notion of time which informs the manner in which the critic conceives of history, representation and criticism itself. This thesis reveals the philosophies of time inherent in certain key modern critical concepts: allegory, irony and the sublime. Each concept opens a breach in time, a disruption of chronology. In each case this gap or aporia is emphatically closed, elided or denied. Taking the philosophy of time elaborated by Giorgio Agamben as an introductory proposition, my argument turns in Chapter One to the allegorical temporality which Walter Benjamin sees as the time of photography. The second chapter examines the aesthetics of the sublime as melancholic or mournful untimeliness. In Chapter Three, Paul de Man's conception of irony provides an exemplary instance of the denial of this troubling temporal predicament. In opposition to the foreclosure of the disturbing temporalities of criticism, history and representation, the thesis proposes a fundamental rethinking of the philosophy of time as it relates to these categories of reflection. In a reading of an inaugural meditation on the nature of time, and in examining certain key contemporary philosophical and critical texts, I argue for a critical attendance to that which eludes those modes of thought that attempt to map time as a recognizable and essentially spatial field. The Confessions of Augustine provide, in the fourth chapter, a model for thinking through the problems set up earlier: Augustine affords us, precisely, a means of conceiving of the gap or the interim. In the final chapter, this concept is developed with reference to the criticism of Arnold and Eliot, the fiction of Virginia Woolf and the philosophy of cinema derived from Deleuze and Lyotard. In conclusion, the philosophical implications of the thesis are placed in relation to a conception of the untimeliness of death
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