25 research outputs found
Optical tweezers with enhanced efficiency based on laser-structured substrates
We present an optical nanotrapping setup that exhibits enhanced efficiency,
based on localized plasmonic fields around sharp metallic features. The
substrates consist of laser-structured silicon wafers with quasi-ordered
microspikes on the surface, coated with a thin silver layer. The resulting
optical traps show orders of magnitude enhancement of the trapping force and
the effective quality factor
Real-time observation of a coherent lattice transformation into a high-symmetry phase
Excursions far from their equilibrium structures can bring crystalline solids
through collective transformations including transitions into new phases that
may be transient or long-lived. Direct spectroscopic observation of
far-from-equilibrium rearrangements provides fundamental mechanistic insight
into chemical and structural transformations, and a potential route to
practical applications, including ultrafast optical control over material
structure and properties. However, in many cases photoinduced transitions are
irreversible or only slowly reversible, or the light fluence required exceeds
material damage thresholds. This precludes conventional ultrafast spectroscopy
in which optical excitation and probe pulses irradiate the sample many times,
each measurement providing information about the sample response at just one
probe delay time following excitation, with each measurement at a high
repetition rate and with the sample fully recovering its initial state in
between measurements. Using a single-shot, real-time measurement method, we
were able to observe the photoinduced phase transition from the semimetallic,
low-symmetry phase of crystalline bismuth into a high-symmetry phase whose
existence at high electronic excitation densities was predicted based on
earlier measurements at moderate excitation densities below the damage
threshold. Our observations indicate that coherent lattice vibrational motion
launched upon photoexcitation with an incident fluence above 10 mJ/cm2 in bulk
bismuth brings the lattice structure directly into the high-symmetry
configuration for tens of picoseconds, after which carrier relaxation and
diffusion restore the equilibrium lattice configuration.Comment: 22 pages, 4 figure
E-Democracy and the European Public Sphere
The chapter starts with an outline of outstanding recent contributions to the discussion of the EU democratic deficit and the so-called “no demos” problem and the debate about European citizenship and European identity—mainly in the light of insights from the EU crisis. This is followed by reflections on the recent discussion on the state of the mass media-based European public sphere. Finally, the author discusses the state of research on the Internet’s capacity to support the emergence of a (renewed) public sphere, with a focus on options for political actors to use the Internet for communication and campaigning, on the related establishment of segmented issue-related publics as well as on social media and its two-faced character as an enabler as well as a distorting factor of the public sphere. The author is sceptic about the capacities of Internet-based political communication to develop into a supranational (European) public sphere. It rather establishes a network of a multitude of discursive processes aimed at opinion formation at various levels and on various issues. The potential of online communication to increase the responsiveness of political institutions so far is set into practice insufficiently. Online media are increasingly used in a vertical and scarcely in a horizontal or interactive manner of communication
GREECE. Critical junctures in the media transformation process.
The present study seeks to identify risks and opportunities for deliberative communication in
Greece and to flag critical junctures in the development of the media between 2000 and 2020
across the four domains covered by the MEDIADELCOM project: a) legal and ethical regulation,
b) journalism, c) media usage patterns, and d) media-related competences. Among the major
forces shaping the development of the media during the period under study, the economic
recession that the country experienced between 2009 and 2018, and the spread of the internet,
certainly stand out. Both these factors had a profound impact on media market structures and
on journalism. The effects of digitalization are also evident in changing media use and supply
practices. Overall, these forces create risks and opportunities for a media system whose development
has been shaped by the close connection between the media and the political system