Increased flexibility in lab-on-chip design with a polymer patchwork approach

Nanofluidic structures are often the key element of many lab-on-chips for biomedical and environmental applications. The demand for these devices to be able to perform increasingly complex tasks triggers a request for increasing the performance of the fabrication methods. Soft lithography and poly(dimethylsiloxane) (PDMS) have since long been the basic ingredients for producing low-cost, biocompatible and flexible devices, replicating nanostructured masters. However, when the desired functionalities require the fabrication of shallow channels, the \u201croof collapse\u201d phenomenon, that can occur when sealing the replica, can impair the device functionalities. In this study, we demonstrate that a \u201cfocused drop-casting\u201d of h-PDMS (hard PDMS) on nanostructured regions, provides the necessary stiffness to avoid roof collapse, without increasing the probability of deep cracks formation, a drawback that shows up in the peel-off step, when h-PDMS is used all over the device area. With this new approach, we efficiently fabricate working devices with reproducible sub-100 nm structures. We verify the absence of roof collapse and deep cracks by optical microscopy and, in order to assess the advantages that are introduced by the proposed technique, the acquired images are compared with those of cracked devices, whose top layer, of h-PDMS, and with those of collapsed devices, made of standard PDMS. The geometry of the critical regions is studied by atomic force microscopy of their resin casts. The electrical resistance of the nanochannels is measured and shown to be compatible with the estimates that can be obtained from the geometry. The simplicity of the method and its reliability make it suitable for increasing the fabrication yield and reducing the costs of nanofluidic polymeric lab-on-chips

Energy in one dimensional linear waves in a string

We consider the energy density and energy transfer in small amplitude, one-dimensional waves on a string, and find that the common expressions used in textbooks for the introductory physics with calculus course give wrong results for some cases, including standing waves. We discuss the origin of the problem, and how it can be corrected in a way appropriate for the introductory calculus based physics course.Comment: 5 page

An off-shell I.R. regularization strategy in the analysis of collinear divergences

We present a method for the analysis of singularities of Feynman amplitudes based on the Speer sector decomposition of the Schwinger parametric integrals combined with the Mellin-Barnes transform. The sector decomposition method is described in some details. We suggest the idea of applying the method to the analysis of collinear singularities in inclusive QCD cross sections in the mass-less limit regularizing the forward amplitudes by an off-shell choice of the initial particle momenta. It is shown how the suggested strategy works in the well known case of the one loop corrections to Deep Inelastic Scattering.Comment: 25 pages, 3 figure

Museums as tools for sustainable community development : a study of four archaeological museums in northern Peru

Funding: This research received funding from the European Union’s Horizon 2020 Research and Innovation programme under grant agreement No. 693669.A new way of defining and managing museums has emerged in the 21st century, with local communities at the heart of the equation. At the same time, communities have become aware of the political and symbolic importance of working with and being represented by museums: not only can such collaborations strengthen local identities and political power, but it can also enable communities to benefit from the potential of museums to attract resources derived from tourism. Within this framework, the team at the Pontifical Catholic University of Peru is participating in the EU-LAC Museums project. As part of the European Union’s Horizon 2020 Programme, the initiative aims to develop community museums, foster links between museums and their communities and carry out projects that strengthen local heritage. The Peruvian team developed its proposal in four community-centred archaeological museums on Peru’s northern coast: the Chan Chan and Huacas de Moche site museums in the region of La Libertad, and the Túcume and Sicán museums in the Lambayeque regions. The project’s objectives are to identify how these museums involve local communities, and the role they play in the social, educational and economic development of surrounding territories. Once identified, the project’s actions aimed to consolidate and strengthen these different forms of interrelation, which encourage sustainability, regional integration, education and the use of technologies. To account properly for the vulnerability of local populations amid catastrophic floods caused by the El Niño phenomenon, it was crucial to apply a territorial perspective. This chapter presents the different experiences and actions carried out in the ‘Peru Case Study’ of the EU-LAC Museums project, highlighting the current impact of four local museums. It also promotes the active participation of the institutions and their communities in the future, using a model of joint heritage management that contributes to local sustainable development.Publisher PDFPeer reviewe

Second harmonic generation on self-assembled GaAs/Au nanowires with thickness gradient

Here we investigated the SH generation at the wavelength of 400 nm (pump laser at 800 nm, 120 fs pulses) of a "metasurface" composed by an alternation of GaAs nano-grooves and Au nanowires capping portions of flat GaAs. The nano-grooves depth and the Au nanowires thickness gradually vary across the sample. The samples are obtained by ion bombardment at glancing angle on a 150 nm Au mask evaporated on a GaAs plane wafer. The irradiation process erodes anisotropically the surface, creating Au nanowires and, at high ion dose, grooves in the underlying GaAs substrate (pattern transfer). The SHG measurements are performed for different pump linear polarization angle at different positions on the "metasurface" in order to explore the regions with optimal conditions for SHG efficiency. The pump polarization angle is scanned by rotating a half-wave retarder plate. While the output SH signal in reflection is analyzed by setting the polarizer in s or p configuration in front of the detector. The best polarization condition for SHG is obtained in the configuration where the pump and second harmonic fields are both p polarized, and the experiments show a SH polarization dependence of the same symmetry of bulk GaAs. Thus, the presence of gold contributes only as field localization effect, but do not contributes directly as SH generator

Evaluation of the program ‘understanding and learning in the classroom’

We present the program “understanding and learning in the classroom” centered on the improvement of reading comprehension strategies. We present also an evaluation of this program

The Formation of Cataclysmic Variables: The Influence of Nova Eruptions

The theoretical and observed populations of pre-cataclysmic variables are dominated by systems with low-mass white dwarfs (WDs), while the WD masses in cataclysmic variables (CVs) are typically high. In addition, the space density of CVs is found to be significantly lower than in the theoretical models. We investigate the influence of nova outbursts on the formation and initial evolution of CVs. In particular, we calculate the stability of the mass transfer in the case where all of the material accreted on the WD is lost in classical novae and part of the energy to eject the material comes from a common-envelope-like interaction with the companion. In addition, we study the effect of an asymmetry in the mass ejection that may lead to small eccentricities in the orbit. We find that a common-envelope-like ejection significantly decreases the stability of the mass transfer, particularly for low-mass WDs. Similarly, the influence of asymmetric mass loss can be important for short-period systems and even more so for low-mass WDs; however, this influence likely disappears long before the next nova outburst due to orbital circularization. In both cases the mass-transfer rates increase, which may lead to observable (and perhaps already observed) consequences for systems that do survive to become CVs. However, a more detailed investigation of the interaction between nova ejecta and the companion and the evolution of slightly eccentric CVs is needed before definite conclusions can be drawn