Time-Reversal Symmetry and Universal Conductance Fluctuations in a Driven Two-Level System

In the presence of time-reversal symmetry, quantum interference gives strong corrections to the electric conductivity of disordered systems. The self-interference of an electron wavefunction traveling time-reversed paths leads to effects such as weak localization and universal conductance fluctuations. Here, we investigate the effects of broken time-reversal symmetry in a driven artificial two-level system. Using a superconducting flux qubit, we implement scattering events as multiple Landau-Zener transitions by driving the qubit periodically back and forth through an avoided crossing. Interference between different qubit trajectories give rise to a speckle pattern in the qubit transition rate, similar to the interference patterns created when coherent light is scattered off a disordered potential. Since the scattering events are imposed by the driving protocol, we can control the time-reversal symmetry of the system by making the drive waveform symmetric or asymmetric in time. We find that the fluctuations of the transition rate exhibit a sharp peak when the drive is time-symmetric, similar to universal conductance fluctuations in electronic transport through mesoscopic systems

Effect of ship locking on sediment oxygen uptake in impounded rivers

In the majority of large river systems, flow is regulated and/or otherwise affected by operational and management activities, such as ship locking. The effect of lock operation on sediment-water oxygen fluxes was studied within a 12.9 km long impoundment at the Saar River (Germany) using eddy-correlation flux measurements. The continuous observations cover a time period of nearly 5 days and 39 individual locking events. Ship locking is associated with the generation of surges propagating back and forth through the impoundment which causes strong variations of near-bed current velocity and turbulence. These wave-induced flow variations cause variations in sediment-water oxygen fluxes. While the mean flux during time periods without lock operation was 0.5 6 0.1 g m�2 d�1, it increased by about a factor of 2 to 1.0 6 0.5 g m�2 d�1 within time periods with ship locking. Following the daily schedule of lock operations, fluxes are predominantly enhanced during daytime and follow a pronounced diurnal rhythm. The driving force for the increased flux is the enhancement of diffusive transport across the sediment-water interface by bottom-boundary layer turbulence and perhaps resuspension. Additional means by which the oxygen budget of the impoundment is affected by lock-induced flow variations are discussed

Letters to a Glacier; An Experiment and Critique of M. Jackson’s Glacier-Ruins Narrative

“Words are events, they do things, change things. They transform both speaker and hearer; they feed energy back and forth and amplify it. They feed understanding or emotion back and forth and amplify it.” —Ursula K. Le Guin Letters to a Glacier; The Buoy Project Isafjordur is an ongoing invitation to the people of Isafjordur to write a letter to a specific glacier in Iceland onto a collection of discarded buoys gathered from the Isafjorudur and Bolungarvik junk yards. Over a period of two days on November 9th and 10th, I actively invited customers in the local cafe Heimabyggð to take part in the project. The project was advertised in various locations around Isafjordur in both English and Icelandic. Places with posters included: The University Center, the hallway between the dance studio and Edinborg, Hamraborg, and Heimabyggð. The event was also advertised on Facebook and Instagram by Heimabyggð. A total of 24 letters were written by the public during this time. The transcript of those letters are included at the bottom of this document. The buoys will be returned to the Isafjordur junkyard, so they might be used as buoys at a future date. I chose buoys as a medium for glacial letter writing because they are widely available objects often seen in fishing or seaport towns. Their natural buoyancy is uplifting. The colors are both fun and alarming. And in the predicted scenario where many Icelandic glaciers will melt, they might meet the water of a glacier, and the glacier can meet the words. In this essay I will critique M. Jackson’s glacier-ruins narrative, and make a case that the role of art in climate discourse is not to make predictive statements, or imagine alternative futures. But instead, it’s role is to reflect and question both its subject matter and the structures that contextualize the art, and provide a space for people to experience and conceptualise our realities through alternative mediums

Psychological sources of response effects in self-administered and telephone surveys

The impact of mode of data collection (self-administered questionnaire vs. telephone interview) on the emergence of response effects and the accuracy of recall from memory was explored in a cross-cultural experiment, conducted in the U.S. and the Federal Republic of Germany. As predicted on the basis of psychological considerations, question order effects were obtained under telephone interview conditions but not under self-administered conditions, where question order is eliminated by the opportunity to browse back and forth through the questionnaire. On the other hand, the impact of the content of related questions was more pronounced under self-administered than under telephone interview conditions, independent of the order in which they were presented. This reflects respondents' differential opportunity to elaborate on related questions under both administration modes, as well as the necessity to rely on the content of presumably related questions in determining the meaning of ambiguous questions under self-administered conditions. Finally, respondents' recall of the date of public events was more accurate under self-administered than under telephone interview conditions, reflecting the beneficial effect of having sufficient time to work on the recall task

Becoming Disabled

This thesis examines the becoming of disabled people’s identities, illustrating the multiple and complex temporalities that shift and move in flux as disabilities, health conditions and illnesses change over time. Understanding disability as an unfolding process of continuous change, the thesis forwards the concept of ‘becoming disabled’ as tying together disabled people’s lived and embodied experiences. An unfolding participatory qualitative research methodology was developed with eight participants and their partners. Four methods were chosen by participants to explore their experiences: drawing participatory timelines, taking photographs through photovoice, talking in conversations and writing diary entries. The research process itself moved back and forth, overlapping and churning through cycles of participation, action and reflection, shaping the subsequent findings, which are arranged under four key themes. ‘Becoming emotional’ explores the gendered and emotional temporalities of events, such as diagnosis, accident and injury, to everyday acts that shape the future. ‘Becoming well’ illustrates the affective capacity of material items to facilitate day-to-day and lifelong recoveries. ‘Becoming mobile’ discusses the pace, speed and rhythm of walking and wheeling. ‘Memories’ of disability, health conditions and illnesses continue to unfold, shaping new possibilities and new futures. The thesis concludes that becoming disabled is an underlying, always present and unfolding process of continuous change, which differs to the fixed and categorical basis of ‘being disabled’ which has characterised much research. Becoming disabled is always reaching forward and never complete, emphasising the intricacies of time, the temporalities, the moments, the transitions and the trajectories of becoming, in everyday life and across the life course. The research sought to examine the everyday practices and processes that shape disabled people’s identities; and to explore the role of the past, the present, and the future in disabled people’s lives. Suggestions are made for future research

On-demand delivery of single DNA molecules using nanopipettes

Understanding the behavioral properties of single molecules or larger scale populations interacting with single molecules is currently a hotly pursued topic in nanotechnology. This arises from the potential such techniques have in relation to applications such as targeted drug delivery, early stage detection of disease, and drug screening. Although label and label-free single molecule detection strategies have existed for a number of years, currently lacking are efficient methods for the controllable delivery of single molecules in aqueous environments. In this article we show both experimentally and from simulations that nanopipets in conjunction with asymmetric voltage pulses can be used for label-free detection and delivery of single molecules through the tip of a nanopipet with “on-demand” timing resolution. This was demonstrated by controllable delivery of 5 kbp and 10 kbp DNA molecules from solutions with concentrations as low as 3 pM

Experimental evidence of ageing and slow restoration of the weak-contact configuration in tilted 3D granular packings

Granular packings slowly driven towards their instability threshold are studied using a digital imaging technique as well as a nonlinear acoustic method. The former method allows us to study grain rearrangements on the surface during the tilting and the latter enables to selectively probe the modifications of the weak-contact fraction in the material bulk. Gradual ageing of both the surface activity and the weak-contact reconfigurations is observed as a result of repeated tilt cycles up to a given angle smaller than the angle of avalanche. For an aged configuration reached after several consecutive tilt cycles, abrupt resumption of the on-surface activity and of the weak-contact rearrangements occurs when the packing is subsequently inclined beyond the previous maximal tilting angle. This behavior is compared with literature results from numerical simulations of inclined 2D packings. It is also found that the aged weak-contact configurations exhibit spontaneous restoration towards the initial state if the packing remains at rest for tens of minutes. When the packing is titled forth and back between zero and near-critical angles, instead of ageing, the weak-contact configuration exhibits "internal weak-contact avalanches" in the vicinity of both the near-critical and zero angles. By contrast, the stronger-contact skeleton remains stable