104 research outputs found
Building Blocks for Wavelength Converters: A Study of Monolithic Devices in Piezoelectric Materials
No full textIn cavity optomechanics, optical fields are coupled to the displacement of mechanical resonators. While it is interesting to study fundamental aspects of this interaction, it is the ability to link this mechanical displacement to various other degrees of freedom that inspires many applications in the field. In these applications, the mechanical resonator can be used as a handle to an external influence for the purpose of sensing, but also as a transducer between two otherwise detached degrees of freedom. The latter approach is the focus of this work. A particularly interesting regime for such a transduction process is between a few-gigahertz microwave tone and optical photons at telecom wavelengths around 1550 nm, connecting the operating regimes of long-range telecommunication with that of superconducting quantum nodes. Bridging the gap between these domains is an essential step towards any size of quantum network based on superconducting nodes, as the losses encountered in microwave transmission lines prohibits the connection of such nodes over length scales extending beyond a few meters. As such, a transducer between the few-gigahertz and optical telecom domains would enable the use of low-loss optical channels to connect remote superconducting nodes, given that the quantum information is preserved throughout the conversion process. One approach of realizing such a converter makes use of a gigahertz-frequency mechanical mode as the transducing element, which is coupled to the optical telecom domain using the optomechanical interaction and to the microwave domain using the electromechanical interaction. In this work, we aim to unify both of these interactions in a single device by designing and fabricating optomechanical devices from the III/V semiconductors, which, alongside their good optical properties, are also piezoelectric. In Chapter 2, we motivate our material choice and introduce the relevant properties of the materials, as well as their impact on the fabrication process. Following the material discussion, we then set out in Chapter 3 to realize a microwave-to-optics converter made of an optomechanical crystal in gallium arsenide, which we resonantly couple to a interdigital transducer using surface-acoustic-waves. With this device, we demonstrate the first microwave-to-optics conversion using a mechanical mode with an average number of thermal excitations below one. As well as verifying the coherence of the conversion process, our experiments also highlight the limitations arising from the material choice due to absorption-induced incoherent heating of the mechanical mode. The material choice itself then becomes the central topic of Chapter 4, where we opt for a gallium phosphide, a relative of gallium arsenide, which prominently features a larger bandgap. With this material we show non-classical correlations between photons an phonons. We enter a a regime that was previously inaccessible to devices made from piezoelectric materials, a promising step towards realizing the noise-requirements for microwave-to-optics converters. In Chapter 5, we use the insights from the two previous chapters to design a new type of electro-opto-mechanical resonator, specifically aimed at microwave-to-optics conversion. We miniaturize the electromechanical interface and use strongly coupled mechanical resonators for the transfer of excitations between the microwave and mechanical mode. We fabricate and characterise initial devices as well as demonstrate the validity of the functioning principle. Finally in Chapter 6, we reflect on the results of the previous chapters and highlight some potential advantages of other approaches
Platform for Measurements of the Casimir Force between Two Superconductors
No full textSeveral experimental demonstrations of the Casimir force between two closely spaced bodies have been realized over the past two decades. Extending the theory to incorporate the behavior of the force between two superconducting films close to their transition temperature has resulted in competing predictions. To date, no experiment exists that can test these theories, partly due to the difficulty in aligning two superconductors in close proximity, while still allowing for a temperature-independent readout of the arising force between them. Here we present an on-chip platform based on an optomechanical cavity in combination with a grounded superconducting capacitor, which overcomes these challenges and opens up the possibility to probe modifications to the Casimir effect between two closely spaced, freestanding superconductors as they transition into a superconducting state. We also perform preliminary force measurements that demonstrate the capability of these devices to probe the interplay between two widely measured quantum effects: Casimir forces and superconductivity.QN/Groeblacher LabDynamics of Micro and Nano System
Über kulturelle Transformationen der Sexual- und Geschlechtsformen in den letzten Jahrzehnten
No full textWestern cultures have witnessed a tremendous cultural and social transformation of sexuality in the years since the sexual revolution. Apart from a few public debates and scandals, the process has moved along gradually and quietly. Yet its real and symbolic effects are probably much more consequential than those generated by the sexual revolution of the sixties. Sigusch refers to the broad-based recoding and reassessment of the sexual sphere during the eighties and nineties as the "neosexual revolution". The neosexual revolution is dismantling the old patterns of sexuality and reassembling them anew. In the process, dimensions, intimate relationships, preferences and sexual fragments emerge, many of which had submerged, were unnamed or simply did not exist before. In general, sexuality has lost much of its symbolic meaning as a cultural phenomenon. Sexuality is no longer the great metaphor for pleasure and happiness, nor is it so greatly overestimated as it was during the sexual revolution. It is now widely taken for granted, much like egotism or motility. Whereas sex was once mystified in a positive sense - as ecstasy and transgression, it has now taken on a negative mystification characterized by abuse, violence and deadly infection. While the old sexuality was based primarily upon sexual instinct, orgasm and the heterosexual couple, neosexualities revolve predominantly around gender difference, thrills, self-gratification and prosthetic substitution. From the vast number of interrelated processes from which neosexualities emerge, three empirically observable phenomena have been selected for discussion here: the dissociation of the sexual sphere, the dispersion of sexual fragments and the diversification of intimate relationships. The outcome of the neosexual revolution may be described as "lean sexuality" and "self-sex".Nach der letzten "sexuellen Revolution" kam es in den reichen Gesellschaften des Westens zu einer enormen kulturellen und sozialen Transformation der Sexualität. Sigusch nennt sie die "neosexuelle Revolution". Bisher ist diese Transformation und Umwertung der Sexualität eher langsam und leise verlaufen. Ihre symbolischen und realen Auswirkungen sind aber möglicherweise einschneidender als die der schnellen und lauten sexuellen Revolution der 1960er und 1970er Jahre. Die neosexuelle Revolution zerlegt die alte Sexualität und setzt sie neu zusammen. Dadurch treten Dimensionen, Intimbeziehungen, Präferenzen und Sexualfragmente hervor, die bisher verschüttet waren, keinen Namen hatten oder gar nicht existierten. Insgesamt verlor die Kulturform Sexualität an symbolischer Bedeutung. Heute ist Sexualität nicht mehr die große Metapher der Lust und des Glücks. Sie wird nicht mehr so stark überschätzt wie zur Zeit der sexuellen Revolution, ist eher eine allgemeine Selbstverständlichkeit wie Egoismus oder Motilität. Während die alte Sexualität positiv mystifiziert wurde als Ekstase und Transgression, wird die neue negativ mystifiziert als Missbrauch, Gewalt und tödliche Infektion. Während die alte Sexualität vor allem aus Trieb, Orgasmus und dem heterosexuellen Paar bestand, bestehen die Neosexualitäten vor allem aus Geschlechterdifferenz, Thrills, Selbstliebe und Prothetisierungen. Aus der Unzahl der miteinander vernetzten Prozesse, die Neosexualitäten hervorbringen, werden drei herausgegriffen: die Dissoziation der sexuellen Sphäre, die Dispersion der sexuellen Fragmente und die Diversifikation der sexuellen Beziehungen. Das Resultat der neosexuellen Revolution könnte als "Lean sexuality" oder als "Selfsex" bezeichnet werden, der selbstdiszipliniert und selbstoptimiert ist
Strahlung von Sendeanlagen und Gesundheit : Bewertung von wissenschaftlichen Studien im Niedrigdosisbereich (Stand: Dezember 2012)
No full textThis report updates the assessment of the health effects of high-frequency radiation based on newly published studies on human beings in the period from October 2006 to December 2012. It takes account of experimental field studies, epidemiological studies of population groups in their everyday environment and experimental studies with short-term exposure under controlled conditions in the laboratory, in which the influence of high-frequency radiation from fixed facilities such as broadcasting transmitters and mobile telephone base stations was studied. In the past six years, approximately 50 studies on this topic were published. Generally speaking, exposure to high-frequency radiation from fixed transmitters is pleasingly low, and at this exposure level no harmful effects on health have been scientifically established to date. In view of this, there is no call for a modification of the ambient limit values specified in the Ordinance relating to Protection from Non-Ionising Radiation (ONIR). With respect to the nonthermal effects of high-frequency radiation, there are still many gaps in scientific knowledge. In particular, there are almost no methodologically sound long-term observations. It is therefore not possible to make a reliable assessment of any potential longterm risks at this time, and consequently caution is called for, especially with regard to long-term exposure to high-frequency radiation
Cool and hot components of a coronal bright point
No full textWe performed a systematic study of the Doppler shifts and electron densities measured in an EUV bright point (hereafter BP) observed in more than 10 EUV lines with formation temperatures from log (T/K) = 4.5 to 6.3. Those parts of a BP seen in transition region and coronal lines are defined as its cool and hot components, respectively. We find that the transition from cool to hot occurs at a temperature around log (T/K) = 5.7. The two components of the BP reveal a totally different orientation and Doppler-shift pattern, which might result from a twist of the associated magnetic loop system. The analysis of magnetic field evolution and topology seems to favor a two-stage heating process, in which magnetic cancellation and separator reconnection are powering, respectively, the cool and hot components of the BP. We also found that the electron densities of both components of the BP are higher than those of the surrounding quiet Sun, and comparable to or smaller than active region densities.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000257661900018&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Astronomy & AstrophysicsSCI(E)24ARTICLE2L121-L12468
H. Wissemann, Untersuchungen zur onomatopoiie, I. teil: Die sprachpsychologischen versuche. Heidelberg 1954, C. Winter
No full textThis publication, which is to be followed by a second volume containing
the application of the theoretical and methodical consequences
of the research described and the principles embodied here, constitutes
a new approach to the partial solution of one of the oldest problems of
linguistic science. Abstaining from both linguistic theory and an
analysis of existing onomatopoeias - since these methods have not
led to leading principles in etymological research concerned with the
expressive constituents of tile vocabulary - the author, following a
previous publication of D. Usnadzes ("Ein experimenteller Beitrag
zum Problem der psychologischen Grundlagen der Namengebung",
Psychol. Forsch. 5, 1924) instituted experiments in order closely to
ascertain how words denoting sounds (Gerauschbenennungen) come
into existence
Gallium Phosphide as a Piezoelectric Platform for Quantum Optomechanics
No full textRecent years have seen extraordinary progress in creating quantum states of mechanical oscillators, leading to great interest in potential applications for such systems in both fundamental as well as applied quantum science. One example is the use of these devices as transducers between otherwise disparate quantum systems. In this regard, a promising approach is to build integrated piezoelectric optomechanical devices that are then coupled to microwave circuits. Optical absorption, low quality factors, and other challenges have up to now prevented operation in the quantum regime, however. Here, we design and characterize such a piezoelectric optomechanical device fabricated from gallium phosphide in which a 2.9 GHz mechanical mode is coupled to a high quality factor optical resonator in the telecom band. The large electronic band gap and the resulting low optical absorption of this new material, on par with devices fabricated from silicon, allows us to demonstrate quantum behavior of the structure. This not only opens the way for realizing noise-free quantum transduction between microwaves and optics, but in principle also from various color centers with optical transitions in the near visible to the telecom band.QN/Groeblacher La
Excitation of kink waves due to small-scale magnetic reconnection in the chromosphere?
No full textThe kink wave, which has often been observed in coronal loops, is considered as a possibly important energy source contributing to coronal heating. However, its generation has not yet been observed. Here, we report the first observation of kink-wave excitation caused by magnetic reconnection as inferred from Solar Optical Telescope measurements made in the Ca II line. We observed transverse-displacement oscillations on a spicule which propagated upwardly along the spicule trace and originated from the cusp of an inverted Y-shaped structure, where apparently magnetic reconnection occurred. Such transverse oscillation of an individual spicule is interpreted by us to be the signature of a kink wave that was excited by magnetic reconnection. We present the height variations of the velocity amplitude, delta v, and the phase speed, C(k), of the kink wave, starting from its source region. The kink wave is found to steepen with height and to evolve into a nonlinear state with a large relative disturbance, yielding a (delta v/C(k)) of 0.21 at 5.5 Mm. This nonlinear kink wave seems to be damped in velocity amplitude beyond 5.5 Mm, which may result from the conversion of transverse-fluctuation energy to longitudinal-motion energy required to sustain the spicule. We also estimate the energy flux density carried by the kink wave, and in spite of its attenuation in the transition region conclude it to be sufficient for heating the quiet corona. Our findings shed new light on future modeling of coronal heating and solar wind acceleration involving magnetic reconnection in the chromosphere.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000271150200026&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Astronomy & AstrophysicsSCI(E)59ARTICLE2L217-L22270
MNDO calculations on diazirines
No full textPT: J; CR: ARCHER WH, 1976, J CHEM SOC F1, V72, P1448 BIGOT B, 1978, IUPAC S PHOTOCHEMIST, P46 BINKLEY JS, QPCE368 BRADLEY GF, 1977, J CHEM SOC P2, P1214 BRASLAVSKY S, 1977, CHEM REV, V77, P473 BURKHOLDER D, J AM CHEM SOC CLOUGH PN, 1970, CAN J CHEM, V48, P2919 DEWAR MJS, J AM CHEM SOC, V99, P4999 DEWAR MJS, 1977, J AM CHEM SOC, V99, P4907 DEWAR MJS, 1978, J AM CHEM SOC, V100, P3607 DEWAR MJS, 1978, J AM CHEM SOC, V100, P777 ENGLEBRECHT WJ, 1975, JS AFRICAN CHEM I, V28, P191 FIGUERA JM, 1978, J CHEM SOC F1, P809 FREY HM, 1966, ADV PHOTOCHEM, V4, P225 FREY HM, 1977, J CHEM SOC F1, P2010 GILBERT JC, 1979, TETRAHEDRON LETT, P4619 HEHRE WJ, 1972, J CHEM PHYS, V56, P2257 HENCHER JL, 1967, J AM CHEM SOC, V89, P5527 JENNINGS BM, 1976, J AM CHEM SOC, V98, P6416 JONES M, 1973, CARBENES, V1 JONES WE, 1973, CHEM REV, V73, P407 JONES WE, 1976, J PHOTOCHEM, V5, P311 JONES WE, 1978, J CHEM SOC F2, V74, P831 LATHAN WA, 1973, FORTSCHR CHEM FORSCH, V40, P1 LAU A, 1964, SPECTROCHIM ACTA, V20, P97 LIU MTH, 1973, CAN J CHEM, V51, P2393 LIU MTH, 1977, CAN J CHEM, V55, P3596 MARTIN M, 1976, REV ROUM CHIM, V21, P31 MEIER H, 1977, ANGEW CHEM INT EDIT, V16, P835 MOFFAT JB, 1978, CHEM DIAZONIUM DIA 1 MOFFAT JB, 1979, J MOL STRUCT, V52, P275 NEWTON MD, 1970, J CHEM PHYS, V52, P4064 PIERCE L, 1962, J AM CHEM SOC, V84, P2651 PITTMAN CU, 1974, J ORG CHEM, V39, P373 SCHARPEN LH, 1969, J CHEM PHYS, V50, P2063 SCHMITZ E, 1964, ANGEW CHEM INT EDIT, V3, P333 SCHMITZ E, 1971, 23RD INT C PUR ALL C, V2, P283 SMITH NP, 1979, J CHEM SOC P2, P213 SNYDER LC, 1969, J AM CHEM SOC, V91, P2189 THIEL W, QCPE353 WOLLRAB JE, 1968, J CHEM PHYS, V49, P2405 WOLLRAB JE, 1969, J CHEM PHYS, V51, P1584 YURTSEVER E, 1974, CHEM PHYS LETT, V25, P605; NR: 43; TC: 5; J9: THEOR CHIM ACTA; PG: 7; GA: JW621Source type: Electronic(1
Ultra-low-noise Microwave to Optics Conversion in Gallium Phosphide
No full textMechanical resonators can act as excellent intermediaries to interface single
photons in the microwave and optical domains due to their high quality factors.
Nevertheless, the optical pump required to overcome the large energy difference
between the frequencies can add significant noise to the transduced signal.
Here we exploit the remarkable properties of thin-film gallium phosphide to
demonstrate bi-directional on-chip conversion between microwave and optical
frequencies, realized by piezoelectric actuation of a Gigahertz-frequency
optomechanical resonator. The large optomechanical coupling and the suppression
of two-photon absorption in the material allows us to operate the device at
optomechanical cooperativities greatly exceeding one. Alternatively, when using
a pulsed upconversion pump, we demonstrate that we induce less than one thermal
noise phonon. We include a high-impedance on-chip matching resonator to mediate
the mechanical load with the 50-Ohm source. Our results establish gallium
phosphide as a versatile platform for ultra-low-noise conversion of photons
between microwave and optical frequencies
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