Nanofluidics at the crossroads

Nanofluidics, the field interested in flows at the smallest scales, has grown at a fast pace, reaching an ever finer control offluidic and ionic transport at the molecular level. Still, artificial pores are far from reaching the wealth of functionalities of biological channels that regulate sensory detection, biological transport and neurostransmission - all while operating at energies comparable to thermal noise. Here, we argue that artificial ionic machinescan be designed by harnessing the entire wealth of phenomena available at the nanoscales and exploiting techniques developped in various fields of physics. As they are generally based on solid-state nanopores, rather than soft membranes and proteins, they should in particular aim at taking advantage of their specific properties such as their electronic structure or their ability to interact with light. These observations call for the design of new ways of probing nanofluidic systems. Nanofluidics is now at the crossroads, there are new avenues to build complex ionic machines and this may allow to develop new functionalities inspired by Nature

Interaction confinement and electronic screening in two-dimensional nanofluidic channels

The transport of fluids at the nanoscale is fundamental to manifold biological and industrial processes, ranging from neurotransmission to ultrafiltration. Yet, it is only recently that well-controlled channels with cross-sections as small as a few molecular diameters became an experimental reality. When aqueous electrolytes are confined within such channels, the Coulomb interactions between the dissolved ions are reinforced due to dielectric contrast at the channel walls: we dub this effect `interaction confinement'. Yet, no systematic way of computing these confined interactions has been proposed beyond the limiting cases of perfectly metallic or perfectly insulating channel walls. Here, we introduce a new formalism, based on the so-called surface response functions, that expresses the effective Coulomb interactions within a two-dimensional channel in terms of the wall's electronic structure, described to any desired level of precision. We use it to demonstrate that in few-nanometer-wide channels, the ionic interactions can be tuned by the wall material's screening length. We illustrate this approach by implementing these interactions in brownian dynamics simulations of a strongly confined electrolyte, and show that the resulting ionic conduction can be adjusted between Ohm's law and a Wien effect behavior. Our results provide a quantitative approach to tuning nanoscale ion transport through the electronic properties of the channel wall material

Chirped Pulse Spectrometer Operating at 200 GHz

The combination of electronic sources operating at high frequencies and modern microwave instrumentation has enabled the recent development of chirped-pulse spectrometers for the millimetre and THz bands. This type of instrument can operate at high resolution which is particularly suited to gas phase rotational spectroscopy. The construction of a chirped pulse spectrometer operating at 200 GHz is described in detail while attention is paid to the phase stability and the data accumulation over many cycles. Validation using carbonyl sulphide has allowed the detection limit of the instrument to be established as function of the accumulation. A large number of OCS transitions were identified using a 10 GHz chirped pulse and include the 6 most abundant isotopologues, the weakest line corresponding to the fundamental R(17) transition of 16 O 13 C 33 S with a line strength of 4.3 x 10-26 cm-1 /(molec.cm-2). The linearity of the system response for different degrees of data accumulation and transition line strength was confirmed over 4 orders of magnitudes. A simple analysis of the time domain data was demonstrated to provide the line broadening coefficient without the need for conversion by a Fourier transform. Finally, the pulse duration is discussed and optimal values are given for both Doppler limited and collisional regimes

Terahertz gas phase spectroscopy using a high finesse Fabry-P\'erot cavity

The achievable instrument sensitivity is a critical parameter for the continued development of THz applications. Techniques such as Cavity-Enhanced Techniques and Cavity Ring Down Spectroscopy have not yet been employed at THz frequency due to the difficulties to construct a high finesse Fabry-P\'erot cavity. Here, we describe such a THz resonator based on a low-loss oversized corrugated waveguide with highly reflective photonic mirrors obtaining a finesse above 3000 around 620 GHz. These components enable a Fabry-Perot THz Absorption Spectrometer with an equivalent interaction length of one kilometer giving access to line intensities as low as 10-27cm- 1/(molecule/cm2) with a S/N ratio of 3. In addition, the intracavity optical power have allowed the Lamb-Dip effect to be studied with a low-power emitter, an absolute frequency accuracy better than 5 kHz can be easily obtained providing an additional solution for rotational spectroscopy.Comment: 7 pages, 4 figure

Recent Developments of an Opto-Electronic THz Spectrometer for High-Resolution Spectroscopy

A review is provided of sources and detectors that can be employed in the THz range before the description of an opto-electronic source of monochromatic THz radiation. The realized spectrometer has been applied to gas phase spectroscopy. Air-broadening coefficients of HCN are determined and the insensitivity of this technique to aerosols is demonstrated by the analysis of cigarette smoke. A multiple pass sample cell has been used to obtain a sensitivity improvement allowing transitions of the volatile organic compounds to be observed. A solution to the frequency metrology is presented and promises to yield accurate molecular line center measurements

The SIB Swiss Institute of Bioinformatics' resources: focus on curated databases

The SIB Swiss Institute of Bioinformatics (www.isb-sib.ch) provides world-class bioinformatics databases, software tools, services and training to the international life science community in academia and industry. These solutions allow life scientists to turn the exponentially growing amount of data into knowledge. Here, we provide an overview of SIB's resources and competence areas, with a strong focus on curated databases and SIB's most popular and widely used resources. In particular, SIB's Bioinformatics resource portal ExPASy features over 150 resources, including UniProtKB/Swiss-Prot, ENZYME, PROSITE, neXtProt, STRING, UniCarbKB, SugarBindDB, SwissRegulon, EPD, arrayMap, Bgee, SWISS-MODEL Repository, OMA, OrthoDB and other databases, which are briefly described in this article

Développement d'un spectromètre térahertz haute résolution (application à la caractérisation de polluants atmosphériques)

Le travail de cette thèse a consisté dans le développement d un spectromètre térahertz continu largement accordable entre 0.3 THz et 3.3 THz avec 100% de couverture spectrale. Les lasers de pompe sont deux diodes à cavité étendue verrouillées respectivement par spectroscopie d absorption saturée de Rubidium et par interférométrie à faible contraste. Cette configuration nous offre une pureté spectrale de 2 MHz pour un temps d acquisition de 10 ms et une précision de fréquence absolue estimée à 100 MHz. Nous avons, avec ce dispositif, effectué une étude de l élargissement collisionnel par l azote et par l oxygène de la molécule de cyanure d hydrogène. Les coefficients calculés d élargissement par l air ont été acceptés pour compléter la base de données HITRAN. Un système de métrologie de fréquence a ensuite été développé pour le verrouillage des lasers de pompe en utilisant un peigne de fréquence. Cette configuration nous donne une pureté spectrale de 200 kHz pour un temps d acquisition à 1 s. La précision de fréquence absolue est estimée à 100 kHz. Des mesures de fréquences de transition rotationnelle de la molécule de sulfure de carbonyle ont été réalisées à l aide de ce dispositif et ont permis d affiner les constantes moléculaires de rotation. De nouveaux types de photomélangeurs développés par l IEMN ont été également caractérisés dans ce travail de thèse, nous donnant des résultats encourageants. Notamment la nouvelle conception verticale associée à une antenne cornet a montré des excellentes performances surtout aux hautes fréquences.The work undertaken in this thesis is to develop a wide-band continuous-wave terahertz spectrometer able to cover 100% of the region extending from 0.3 to 3.3 THz. Two extended cavity laser diodes have been frequency stabilized, one to a saturated absorption feature of Rubidium and one to a low contrast Fabry-Perot etalon. This solution yielded a spectral purity of 2 MHz for a 10 ms gate time and an absolute frequency accuracy of 100 MHz. The collisional broadening coefficients of hydrogen cyanide with oxygen and nitrogen were measured. The resulting air-broadening coefficients have been included in the latest version of the HITRAN database. Subsequently a frequency metrology system was developed using a frequency comb and demonstrated an improved source spectral purity evaluated to be 200 kHz for a sweep time of 1 s. The estimated accuracy of absolute frequency is 100 kHz. The measurement of the frequencies of carbonyl sulfide has shown an improvement in the rotational molecular parameters. Several novel photomixer devices fabricated by the IEMN were also characterized in this work with encouraging results. Particularly the novel vertical design combined with a horn antenna showed excellent performance especially at high frequencies.DUNKERQUE-BU Lettres Sci.Hum. (591832101) / SudocSudocFranceF

Modeling of emergent memory and voltage spiking in ionic transport through angstrom-scale slits

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