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Christoph Becker

Publications and source records attributed to Christoph Becker.

At least 37 records · Page 2Linked to original sources
arXiv2020

Proca-stinated Cosmology I: A N-body code for the vector Galileon

We investigate the nonlinear growth of large-scale structure in the generalised Proca theory, in which a self-interacting massive vector field plays the role of driving the acceleration of the cosmic expansion. Focusing to the Proca Lagrangian at cubic order -- the cubic vector Galileon model -- we derive the simplified equations for gravity as well as the longitudinal and transverse modes of the vector field under the weak-field and quasi-static approximations, and implement them in a modified version of the ECOSMOG N-body code. Our simulations incorporate the Vainshtein screening effect, which reconciles the fifth force propagated by the longitudinal mode of the cubic vector Galileon model with local tests of gravity. The results confirm that for all scales probed by the simulation, the transverse mode has a negligible impact on structure formation in a realistic cosmological setup. It is well known that in this model the strength of the fifth force is controlled by a free model parameter, which we denote as beta_3. By running a suite of cosmological simulations for different values of beta_3, we show that this parameter also determines the effectiveness of the Vainshtein screening. The model behaves identically to the cubic scalar Galileon for beta_3 going to zero, in which the fifth force is strong in unscreened regions but is efficiently screened in high-density regions. In the opposite limit, beta_3 going to infinity, the model approaches its `quintessence' counterpart, which has a vanishing fifth force but a modified expansion history compared to LambdaCDM. This endows the model with rich phenomenology, which will be investigated in future works.

astro-ph.CO↗
arXiv2020

Beware the Normative Fallacy

Behavioral research can provide important insights for SE practices. But in performing it, many studies of SE are committing a normative fallacy - they misappropriate normative and prescriptive theories for descriptive purposes. The evidence from reviews of empirical studies of decision making in SE suggests that the normative fallacy may is common. This article draws on cognitive psychology and behavioral economics to explains this fallacy. Because data collection is framed by narrow and empirically invalid theories, flawed assumptions baked into those theories lead to misleading interpretations of observed behaviors and ultimately, to invalid conclusions and flawed recommendations. Researchers should be careful not to rely solely on engineering methods to explain what people do when they do engineering. Instead, insist that descriptive research be based on validated descriptive theories, listen carefully to skilled practitioners, and only rely on validated findings to prescribe what they should do.

cs.SE↗
arXiv2020

A cavity optomechanical locking scheme based on the optical spring effect

We present a novel locking scheme for active length-stabilization and frequency detuning of a cavity optomechanical device based on the optical spring effect. The scheme can be used as an alternative to the Pound-Drever-Hall locking technique but in contrast doesn't require signal processing on time-scales of the cavity decay rate. It is therefore particularly suited for stabilizing micro cavities, where this time-scale can be extremely fast. The error signal is generated through the optical spring effect, i.e. the detuning-dependent frequency-shift of a nanomechanical oscillator that is dispersively coupled to the intra-cavity light field. We explain the functional principle of the lock and characterize its performance in terms of bandwidth and gain profile. The optical spring locking scheme can be implemented without larger efforts in a wide variety of optomechanical systems in the unresolved sideband regime.

physics.ins-det↗
arXiv2019

Critical Requirements Engineering in Practice

The design of software systems inevitably enacts normative boundaries around the site of intervention. These boundaries are, in part, a reflection of the values, ethics, power, and politics of the situation and the process of design itself. This paper argues that Requirements Engineering (RE) require more robust frameworks and techniques to navigate the values implicit in systems design work. To this end, we present the findings from a case of action research where we employed Critical Systems Heuristics (CSH), a framework from Critical Systems Thinking (CST) during requirements gathering for Homesound, a system to safeguard elderly people living alone while protecting their autonomy. We use categories from CSH to inform expert interviews and reflection, showing how CSH can be simply combined with RE techniques (such as the Volere template) to explore and reveal the value-judgements underlying requirements.

cs.SE↗
arXiv2019

Temporal Discounting in Software Engineering: A Replication Study

Background: Many decisions made in Software Engineering practices are intertemporal choices: trade-offs in time between closer options with potential short-term benefit and future options with potential long-term benefit. However, how software professionals make intertemporal decisions is not well understood. Aim: This paper investigates how shifting time frames influence preferences in software projects in relation to purposefully selected background factors. Method: We investigate temporal discounting by replicating a questionnaire-based observational study. The replication uses a changed-population and -experimenter design to increase the internal and external validity of the original results. Results: The results of this study confirm the occurrence of temporal discounting in samples of both professional and student participants from different countries and demonstrate strong variance in discounting between study participants. We found that professional experience influenced discounting. Participants with broader professional experience exhibited less discounting than those with narrower experience. Conclusions: The results provide strong empirical support for the relevance and importance of temporal discounting in SE and the urgency of targeted interdisciplinary research to explore the underlying mechanisms and their theoretical and practical implications. The results suggest that technical debt management could be improved by increasing the breadth of experience available for critical decisions with long-term impact. In addition, the present study provides a methodological basis for replicating temporal discounting studies in software engineering.

cs.SE↗
arXiv2019

Sidewalk and Toronto: Critical Systems Heuristics and the Smart City

`Smart cities', urban development projects that design computational systems and sensory technology to monitor activity and regulate energy consumption and resource distribution, are a frontier for the prospective deployment of ICTs for sustainability. Often reduced to technological problems of optimization, these projects have implications far beyond narrow environmental and consumptive frames of sustainability. Studying them requires frameworks that support us in examining technological and environmental sustainability dimensions jointly with social justice perspectives. This paper uses Critical Systems Heuristics (CSH) to examine the design of Sidewalk Toronto, an ongoing smart city development. We explore how the professed values guiding the project are contentiously enacted, and we argue that key stakeholders and beneficiaries in the planning process significantly constrain the emancipatory and transformative potential of the project by marginalizing the role of residents in determining project purposes. This analysis contributes an example that illustrates the relevance of critical systems thinking in ICT4S and offers CSH as a conceptual frame that supports critical reflection on the tensions between the visions and realities of `sustainable' ways of organizing human life.

cs.CY↗
arXiv2019

Temporal Discounting in Technical Debt: How do Software Practitioners Discount the Future?

Technical Debt management decisions always imply a trade-off among outcomes at different points in time. In such intertemporal choices, distant outcomes are often valued lower than close ones, a phenomenon known as temporal discounting. Technical Debt research largely develops prescriptive approaches for how software engineers should make such decisions. Few have studied how they actually make them. This leaves open central questions about how software practitioners make decisions. This paper investigates how software practitioners discount uncertain future outcomes and whether they exhibit temporal discounting. We adopt experimental methods from intertemporal choice, an active area of research. We administered an online questionnaire to 33 developers from two companies in which we presented choices between developing a feature and making a longer-term investment in architecture. The results show wide-spread temporal discounting with notable differences in individual behavior. The results are consistent with similar studies in consumer behavior and raise a number of questions about the causal factors that influence temporal discounting in software engineering. As the first empirical study on intertemporal choice in SE, the paper establishes an empirical basis for understanding how software developers approach intertemporal choice and provides a blueprint for future studies.

cs.SE↗
arXiv2018

An analysis of Principle 1.2 in the new ACM Code Of Ethics

The new ACM Code of Ethics is a much-needed update, but introduced changes to a central principle that have not been discussed widely enough. This commentary aims to contribute to an improvement of the ethical standards we want computing professionals to aspire to by analyzing how changes introduced to Principle 1.2, Avoid Harm, affect the Code as a whole. The analysis shows that the principle is now internally inconsistent in structure and externally inconsistent with Principle 2.3. It condones intentional harm too broadly and does not oblige those responsible to seek external justification. The existing Principle 2.3 clearly suggests that Principle 1.2 is unethical. As a consequence, the change introduced to Principle 1.2 in the new Code of Ethics nullifies the good intention of the code; counteracts the many good changes introduced in all three drafts; and places the ACM in a dangerous moral position. This short paper explains why and recommends concrete actions.

cs.CY↗
arXiv2018

Identifying Quantum Phase Transitions using Artificial Neural Networks on Experimental Data

Machine learning techniques such as artificial neural networks are currently revolutionizing many technological areas and have also proven successful in quantum physics applications. Here we employ an artificial neural network and deep learning techniques to identify quantum phase transitions from single-shot experimental momentum-space density images of ultracold quantum gases and obtain results, which were not feasible with conventional methods. We map out the complete two-dimensional topological phase diagram of the Haldane model and provide an accurate characterization of the superfluid-to-Mott-insulator transition in an inhomogeneous Bose-Hubbard system. Our work points the way to unravel complex phase diagrams of general experimental systems, where the Hamiltonian and the order parameters might not be known.

cond-mat.quant-gas↗
arXiv2018

Combined feedback and sympathetic cooling of a mechanical oscillator coupled to ultracold atoms

A promising route to novel quantum technologies are hybrid quantum systems, which combine the advantages of several individual quantum systems. We have realized a hybrid atomic-mechanical experiment consisting of a SiN membrane oscillator cryogenically precooled to 500 mK and optically coupled to a cloud of laser cooled Rb atoms. Here, we demonstrate active feedback cooling of the oscillator to a minimum mode occupation of n = 16 corresponding to a mode temperature of T = 200 μK. Furthermore, we characterize in detail the coupling of the membrane to the atoms by means of sympathetic cooling. By simultaneously applying both cooling methods we demonstrate the possibility of preparing the oscillator near the motional ground state while it is coupled to the atoms. Realistic modifications of our setup will enable the creation of a ground state hybrid quantum system, which opens the door for coherent quantum state transfer, teleportation and entanglement as well as quantum enhanced sensing applications.

quant-ph↗
arXiv2018

Dynamics of Ultracold Quantum Gases in the Dissipative Fermi-Hubbard Model

We employ metastable ultracold $^{173}$Yb atoms to study dynamics in the 1D dissipative Fermi-Hubbard model experimentally and theoretically, and observe a complete inhibition of two-body losses after initial fast transient dynamics. We attribute the suppression of particle loss to the dynamical generation of a highly entangled Dicke state. For several lattice depths and for two- and six-spin component mixtures we find very similar dynamics, showing that the creation of strongly correlated states is a robust and universal phenomenon. This offers interesting opportunities for precision measurements.

cond-mat.quant-gas↗
arXiv2017

A millikelvin all-fiber cavity optomechanical apparatus for merging with ultra-cold atoms in a hybrid quantum system

We describe the construction of an apparatus designed to realize a hybrid quantum system comprised of a cryogenically cooled mechanical oscillator and ultra-cold $^{87}$Rb atoms coupled via light. The outstanding feature of our instrument is an in-situ adjustable asymmetric all-fiber membrane-in-the-middle cavity located inside an ultra-high vacuum dilution refrigerator based cryostat. We show that Bose-Einstein condensates of $N=2\times10^6$ atoms can be produced in less than 20 s and demonstrate a single photon optomechanical coupling strength of $g_0=2π\times9$ kHz employing a high-stress Si$_3$N$_4$ membrane with a mechanical quality factor $Q_{\rm m}>10^7$ at a cavity set-up temperature of $T_{\rm MiM}=480$ mK.

physics.ins-det↗
arXiv2017

A Systematic Literature Review on Intertemporal Choice in Software Engineering - Protocol and Results

When making choices in software projects, engineers and other stakeholders engage in decision making that involves uncertain future outcomes. Research in psychology, behavioral economics and neuroscience has questioned many of the classical assumptions of how such decisions are made. This literature review aims to characterize the assumptions that underpin the study of these decisions in Software Engineering. We identify empirical research on this subject and analyze how the role of time has been characterized in the study of decision making in SE. The literature review aims to support the development of descriptive frameworks for empirical studies of intertemporal decision making in practice.

cs.SE↗
arXiv2017

Investigation of Feshbach Resonances in ultra-cold 40 K spin mixtures

Magnetically-tunable Feshbach resonances are an indispensable tool for experiments with atomic quantum gases. We report on twenty thus far unpublished Feshbach resonances and twenty one further probable Feshbach resonances in spin mixtures of ultracold fermionic 40 K with temperatures well below 100 nK. In particular, we locate a broad resonance at B=389.6 G with a magnetic width of 26.4 G. Here 1 G=10^-4 T. Furthermore, by exciting low-energy spin waves, we demonstrate a novel means to precisely determine the zero crossing of the scattering length for this broad Feshbach resonance. Our findings allow for further tunability in experiments with ultracold 40 K quantum gases.

cond-mat.quant-gas↗
arXiv2015

Protective capping of topological surface states of intrinsically insulating Bi$_2$Te$_3$

We have identified epitaxially grown elemental Te as a capping material that is suited to protect the topological surface states of intrinsically insulating Bi$_2$Te$_3$. By using angle-resolved photoemission, we were able to show that the Te overlayer leaves the dispersive bands of the surface states intact and that it does not alter the chemical potential of the Bi$_2$Te$_3$ thin film. From in-situ four-point contact measurements, we observed that the conductivity of the capped film is still mainly determined by the metallic surface states and that the contribution of the capping layer is minor. Moreover, the Te overlayer can be annealed away in vacuum to produce a clean Bi$_2$Te$_3$ surface in its pristine state even after the exposure of the capped film to air. Our findings will facilitate well-defined and reliable ex-situ experiments on the properties of Bi$_2$Te$_3$ surface states with nontrivial topology.

cond-mat.mtrl-sci↗
arXiv2015

The Role of Mode Match in Asymmetric Fiber Cavities

We study and realize asymmetric fiber-based cavities with optimized mode match to achieve high reflectivity on resonance. This is especially important for mutually coupling two physical systems via light fields, e.g. in quantum hybrid systems. Our detailed theoretical and experimental analysis reveals that on resonance the interference effect between the directly reflected non-modematched light and the light leaking back out of the cavity can lead to large unexpected losses due to the mode filtering of the incoupling fiber. Strong restrictions for the cavity design result out of this effect and we show that planar-concave cavities are clearly best suited. We validate our analytical model using numerical calculations and demonstrate an experimental realization of an asymmetric fiber Fabry-Pérot cavity with optimized parameters.

physics.optics↗
arXiv2015

The Karlskrona manifesto for sustainability design

Sustainability is a central concern for our society, and software systems increasingly play a central role in it. As designers of software technology, we cause change and are responsible for the effects of our design choices. We recognize that there is a rapidly increasing awareness of the fundamental need and desire for a more sustainable world, and there is a lot of genuine goodwill. However, this alone will be ineffective unless we come to understand and address our persistent misperceptions. The Karlskrona Manifesto for Sustainability Design aims to initiate a much needed conversation in and beyond the software community by highlighting such perceptions and proposing a set of fundamental principles for sustainability design.

cs.SE↗