Rigid impacts of three-dimensional rocking structures

Studies of rocking motion aim to explain the remarkable earthquake resistance of rocking structures. State-of-the-art assessment methods are mostly based on planar models, despite ongoing efforts to understand the significance of three-dimensionality. Impacts are essential components of rocking motion. We present experimental measurements of free-rocking blocks on a rigid surface, focusing on extreme sensitivity of impacts to geometric imperfections, unpredictability, and the emergence of three-dimensional motion via spontaneous symmetry breaking. These results inspire the development of new impact models of three-dimensional facet and edge impacts of polyhedral objects. Our model is a natural generalization of existing planar models based on the seminal work of George W. Housner. Model parameters are estimated empirically for rectangular blocks. Finally, new perspectives in earthquake assessment of rocking structures are discussed.

Sensing gravity, the quantum way

Devices that exploit the extreme sensitivity of quantum states are making their way out of the lab and into everything from construction and healthcare to seismology. Michael Allen learns more about the technology that goes into building a quantum gravity sensor, and its multitude of uses in research and industry.

Triple descent and the two kinds of overfitting: where and why do they appear?*

A recent line of research has highlighted the existence of a ‘double descent’ phenomenon in deep learning, whereby increasing the number of training examples N causes the generalization error of neural networks (NNs) to peak when N is of the same order as the number of parameters P. In earlier works, a similar phenomenon was shown to exist in simpler models such as linear regression, where the peak instead occurs when N is equal to the input dimension D. Since both peaks coincide with the interpolation threshold, they are often conflated in the literature. In this paper, we show that despite their apparent similarity, these two scenarios are inherently different. In fact, both peaks can co-exist when NNs are applied to noisy regression tasks. The relative size of the peaks is then governed by the degree of nonlinearity of the activation function. Building on recent developments in the analysis of random feature models, we provide a theoretical ground for this sample-wise triple descent. As shown previously, the nonlinear peak at N = P is a true divergence caused by the extreme sensitivity of the output function to both the noise corrupting the labels and the initialization of the random features (or the weights in NNs). This peak survives in the absence of noise, but can be suppressed by regularization. In contrast, the linear peak at N = D is solely due to overfitting the noise in the labels, and forms earlier during training. We show that this peak is implicitly regularized by the nonlinearity, which is why it only becomes salient at high noise and is weakly affected by explicit regularization. Throughout the paper, we compare analytical results obtained in the random feature model with the outcomes of numerical experiments involving deep NNs.

Revisiting Surface Enhanced Raman Scattering on Flat Metallic Surfaces

<p>Surface enhanced Raman spectroscopy (SERS) is undoubtedly a powerful tool as it allows one to overcome the major disadvantage of Raman spectroscopy: the weakness of its signal. Enhancement factors (EF) of up to 1010 make it even possible to detect single molecules. However, using it as an analytical tool to make reproducible, quantitative measurements has so far been difficult as the enhancement of the signal is "bought" at the expense of reproducibility: The larger the EF the more the reproducibility of the substrate suffers. This has been dubbed informally the "SERS uncertainty principle" by Natan [1]. While currently a lot of research effort is taking place at the high-EF-side of the spectrum and ever more sophisticated SERS substrates are being explored, in this thesis we would like to make a shift in paradigm and revisit SERS on flat metallic surfaces, which arguably constitute the simplest substrates available. To this end we will show their usefulness in making quantitative measurements and how they are an ideal platform for a new hybrid technique that combines reproducibility and extreme sensitivity with substantial EFs. For making quantitativemeasurements two examples are explored in a systematic way: in the first example (Chapter 2) the determination of an unknown, resonant Raman cross-section is demonstrated on flat metallic films (possibly with some surface roughness) and confirmed with measurements done on more commonly used SERS substrates. Here the quantitative measurement is made possible by introducing a reference molecule as a standard and having statistics as our main ally: even though we do not know the exact EF that the individual molecules experience on the various substrates, we know that on average both, the unknown sample and the known reference, experience the same. In the second example (Chapter 3) we use commercially available flat films for which we verify experimentally that surface roughness is irrelevant. By themselves these substrates yield no enhancement – in fact they even quench the Raman signal. Yet they allow us to calculate and control the electric field on the surface which enables us to determine the orientation of adsorbed molecules by using surface selection rules (SSR). While the first example is mostly empirical, the second one allows us to test our theoretical understanding of plasmonic systems with proper numerical calculations that are in excellent agreement with the observed data. Finally, in Chapter 4, we use those flat films in a special configuration (called the Kretschmann configuration) to excite Surface Plasmon-Polaritons (SPP). This not only allows us to combine the spatial homogeneity of a flat surface with useful EFs easily predicted fromtheory but also to combine the extreme sensitivity of surface plasmon resonance spectroscopy (SPRS) with the analytical power of SERS. It is not our intention to claim that the work presented here is the first attempt to do analytical work with SERS. Rather the newmethods presented in this thesis will add new strategies and tools to the current research effort while the detailed analysis will provide the means to understand them theoretically and in their historical context.</p>

Revisiting Surface Enhanced Raman Scattering on Flat Metallic Surfaces

<p>Surface enhanced Raman spectroscopy (SERS) is undoubtedly a powerful tool as it allows one to overcome the major disadvantage of Raman spectroscopy: the weakness of its signal. Enhancement factors (EF) of up to 1010 make it even possible to detect single molecules. However, using it as an analytical tool to make reproducible, quantitative measurements has so far been difficult as the enhancement of the signal is "bought" at the expense of reproducibility: The larger the EF the more the reproducibility of the substrate suffers. This has been dubbed informally the "SERS uncertainty principle" by Natan [1]. While currently a lot of research effort is taking place at the high-EF-side of the spectrum and ever more sophisticated SERS substrates are being explored, in this thesis we would like to make a shift in paradigm and revisit SERS on flat metallic surfaces, which arguably constitute the simplest substrates available. To this end we will show their usefulness in making quantitative measurements and how they are an ideal platform for a new hybrid technique that combines reproducibility and extreme sensitivity with substantial EFs. For making quantitativemeasurements two examples are explored in a systematic way: in the first example (Chapter 2) the determination of an unknown, resonant Raman cross-section is demonstrated on flat metallic films (possibly with some surface roughness) and confirmed with measurements done on more commonly used SERS substrates. Here the quantitative measurement is made possible by introducing a reference molecule as a standard and having statistics as our main ally: even though we do not know the exact EF that the individual molecules experience on the various substrates, we know that on average both, the unknown sample and the known reference, experience the same. In the second example (Chapter 3) we use commercially available flat films for which we verify experimentally that surface roughness is irrelevant. By themselves these substrates yield no enhancement – in fact they even quench the Raman signal. Yet they allow us to calculate and control the electric field on the surface which enables us to determine the orientation of adsorbed molecules by using surface selection rules (SSR). While the first example is mostly empirical, the second one allows us to test our theoretical understanding of plasmonic systems with proper numerical calculations that are in excellent agreement with the observed data. Finally, in Chapter 4, we use those flat films in a special configuration (called the Kretschmann configuration) to excite Surface Plasmon-Polaritons (SPP). This not only allows us to combine the spatial homogeneity of a flat surface with useful EFs easily predicted fromtheory but also to combine the extreme sensitivity of surface plasmon resonance spectroscopy (SPRS) with the analytical power of SERS. It is not our intention to claim that the work presented here is the first attempt to do analytical work with SERS. Rather the newmethods presented in this thesis will add new strategies and tools to the current research effort while the detailed analysis will provide the means to understand them theoretically and in their historical context.</p>

Xeroderma Pigmentosum: General Aspects and Management

Xeroderma Pigmentosum (XP) is a rare genetic syndrome with a defective DNA nucleotide excision repair. It is characterized by (i) an extreme sensitivity to ultraviolet (UV)-induced damages in the skin and eyes; (ii) high risk to develop multiple skin tumours; and (iii) neurologic alterations in the most severe form. To date, the management of XP patients consists of (i) early diagnosis; (ii) a long-life protection from ultraviolet radiation, including avoidance of unnecessary UV exposure, wearing UV blocking clothing, and use of topical sunscreens; and (iii) surgical resections of skin cancers. No curative treatment is available at present. Thus, in the last decade, in order to prevent or delay the progression of the clinical signs of XP, numerous strategies have been proposed and tested, in some cases, with adverse effects. The present review provides an overview of the molecular mechanisms featuring the development of XP and highlights both advantages and disadvantages of the clinical approaches developed throughout the years. The intention of the authors is to sensitize scientists to the crucial aspects of the pathology that could be differently targeted. In this context, the exploration of the process underlining the conception of liposomal nanocarriers is reported to focus the attention on the potentialities of liposomal technology to optimize the administration of chemoprotective agents in XP patients.

Narwhals react to ship noise and airgun pulses embedded in background noise

Anthropogenic activities are increasing in the Arctic, posing a threat to niche-conservative species with high seasonal site fidelity, such as the narwhal Monodon monoceros . In this controlled sound exposure study, six narwhals were live-captured and instrumented with animal-borne tags providing movement and behavioural data, and exposed to concurrent ship noise and airgun pulses. All narwhals reacted to sound exposure with reduced buzzing rates, where the response was dependent on the magnitude of exposure defined as 1/distance to ship. Buzzing rate was halved at 12 km from the ship, and whales ceased foraging at 7–8 km. Effects of exposure could be detected at distances > 40 km from the ship.At only a few kilometres from the ship, the received high-frequency cetacean weighted sound exposure levels were below background noise indicating extreme sensitivity of narwhals towards sound disturbance and demonstrating their ability to detect signals embedded in background noise. The narwhal's reactions to sustained disturbance may have a plethora of consequences both at individual and population levels. The observed reactions of the whales demonstrate their auditory sensitivity but also emphasize, that anthropogenic activities in pristine narwhal habitats needs to be managed carefully if healthy narwhal populations are to be maintained.

Calling the Amino Acid Sequence of a Protein/Peptide from the Nanospectrum Produced by a Sub-nanometer Diameter Pore

The blockade current that develops when a protein translocates across a thin membrane through a sub-nanometer diameter pore (i.e., a nanospectrum) informs with extreme sensitivity on the sequence of amino acids that constitute the protein. Whereas mass spectrometry (MS) is still the dominant technology for protein identification, it suffers limitations. In proteome-wide studies, MS fails to sequence proteins de novo, but merely classifies a protein and it is not very sensitive requiring about a femtomole to do that. Compared with MS, a sub-nanometer diameter pore (i.e. a sub-nanopore) directly reads the amino acids constituting a single protein molecule, but efficient computational tools are still required for processing and interpreting the blockade current. Here, we delineate computational methods for processing sub-nanopore nanospectra and predicting electrical blockade currents from protein sequences, which are essential for protein identification.