The New IR FEL Facility at the Fritz-Haber-Institut in Berlin

A mid-infrared oscillator FEL has been commissioned at the Fritz-Haber-Institut. The accelerator consists of a thermionic gridded gun, a subharmonic buncher and two S-band standing-wave copper structures [1,2]. It provides a final electron energy adjustable from 15 to 50 MeV, low longitudinal (<50 keV-ps) and transverse emittance (<20 π mm-mrad), at more than 200 pC bunch charge with a micro-pulse repetition rate of 1 GHz and a macro-pulse length of up to 15 μs. Regular user operation started in Nov. 2013 with 6 user stations. Pulsed radiation with up to 100 mJ macro-pulse energy at about 0.5% FWHM bandwidth is routinely produced in the wavelength range from 4 to 48 μm. We will describe the FEL design and its performance as determined by IR power, bandwidth, and micro-pulse length measurements. Further, an overview of the new FHI FEL facility and first user results will be given. The latter include, for instance, spectroscopy of bio-molecules (peptides and small proteins) conformer selected or embedded in superfluid helium nano-droplets at 0.4 K, as well as vibrational spectroscopy of mass-selected metal-oxide clusters and protonated water clusters in the gas phase

Commissioning Status of the Fritz Haber Institute THz FEL

The THz Free-Electron Laser (FEL) at the Fritz Haber Institute (FHI) of the Max Planck Society in Berlin is designed to deliver radiation from 3 to 300 microns using a single-plane-focusing mid-IR undulator and a two-plane-focusing far-IR undulator that acts as a waveguide for the optical mode. A key aspect of the accelerator performance is the low longitudinal emittance, < 50 keV-psec, that is specified to be delivered at 200 pC bunch charge and 50 MeV from a gridded thermionic electron source. We utilize twin accelerating structures separated by a chicane to deliver the required performance over the < 20 - 50 MeV energy range. The first structure operates at near fixed field while the second structure controls the output energy, which, under some conditions, requires running in a decelerating mode. "First Light" is targeted for the centennial of the sponsor in October 2011 and we will describe progress in the commissioning of this device to achieve this goal. Specifically, the measured performance of the accelerated electron beam will be compared to design simulations and the observed matching of the beam to the mid-IR wiggler will be described

First Lasing of the IR FEL at the Fritz-Haber-Institut Berlin

A new mid-infrared FEL has been commissioned at the Fritz-Haber-Institut in Berlin. The oscillator FEL operates with 15 – 50 MeV electrons from a normal-conducting Sband linac. Calculations of the FEL gain and IR-cavity losses predict that lasing will be possible in the wavelength range from less than 4 to more than 50 μm. First lasing was achieved at a wavelength of 16 μm with an electron energy of 28 MeV. At these conditions, lasing was observed over a cavity length scan range of 100 μm

Status of the Fritz Haber Institute THz FEL

The THz FEL at the Fritz Haber Institute (FHI) in Berlin is designed to deliver radiation from 4 to 400 microns. A single-plane-focusing undulator combined with a 5.4 m long cavity is used is the mid-IR (< 50 micron), while a two-plane-focusing undulator in combination with a 7.2 m long cavity with a 1-d waveguide for the optical mode is used for the far-IR. A key aspect of the accelerator performance is low longitudinal emittance, < 50 keV-psec, at 200 pC bunch charge and 50 MeV from a gridded thermionic electron source. We utilize twin accelerating structures separated by a chicane to deliver the required performance over the < 20 - 50 MeV energy range. The first structure operates at near fixed field while the second structure controls the output energy, which, under some conditions, requires running in a decelerating mode. "First Light" is targeted for the centennial of the FHI in October 2011 and we will describe progress in the commissioning of this device. Specifically, the measured performance of the accelerated electron beam will be compared to design simulations and the observed matching of the beam to the mid-IR wiggler will be described

Patrolling on Dynamic Ring Networks

We study the problem of patrolling the nodes of a network collaboratively by a team of mobile agents, such that each node of the network is visited by at least one agent once in every $I(n)$ time units, with the objective of minimizing the idle time $I(n)$. While patrolling has been studied previously for static networks, we investigate the problem on dynamic networks with a fixed set of nodes, but dynamic edges. In particular, we consider 1-interval-connected ring networks and provide various patrolling algorithms for such networks, for $k=2$ or $k>2$ agents. We also show almost matching lower bounds that hold even for the best starting configurations. Thus, our algorithms achieve close to optimal idle time. Further, we show a clear separation in terms of idle time, for agents that have prior knowledge of the dynamic networks compared to agents that do not have such knowledge. This paper provides the first known results for collaborative patrolling on dynamic graphs

Complexity and Online Algorithms for Minimum Skyline Coloring of Intervals

Graph coloring has been studied extensively in the literature. The classical problem concerns the number of colors used. In this paper, we focus on coloring intervals where the input is a set of intervals and two overlapping intervals cannot be assigned the same color. In particular, we are interested in the setting where there is an increasing cost associated with using a higher color index. Given a set of intervals (on a line) and a coloring, the cost of the coloring at any point is the cost of the maximum color index used at that point and the cost of the overall coloring is the integral of the cost over all points on the line. The objective is to assign a valid color to each interval and minimize the total cost of the coloring. Intuitively, the maximum color index used at each point forms a skyline and so the objective is to obtain a minimum skyline coloring. The problem arises in various applications including optical networks and job scheduling. Alicherry and Bhatia defined in 2003 a more general problem in which the colors are partitioned into classes and the cost of a color depends solely on its class. This problem is NP-hard and the reduction relies on the fact that some color class has more than one color. In this paper we show that when each color class only contains one color, this simpler setting remains NP-hard via a reduction from the arc coloring problem. In addition, we initiate the study of the online setting and present an asymptotically optimal online algorithm. We further study a variant of the problem in which the intervals are already partitioned into sets and the objective is to assign a color to each set such that the total cost is minimum. We show that this seemingly easier problem remains NP-hard by a reduction from the optimal linear arrangement problem

VARC endpoint definition compliance rates in contemporary transcatheter aortic valve implantation studies.

AIMS The Valve Academic Research Consortium (VARC) endpoint definitions were established to standardise the reporting of clinical outcomes following transcatheter aortic valve implantation (TAVI). It remains unclear, however, to what extent and in which manner these definitions are applied. Therefore, we sought to investigate the utilisation and adherence to VARC guidelines since their introduction in 2011 across peerreviewed TAVI-related publications. METHODS AND RESULTS We performed a systematic literature review to identify TAVI-related manuscripts published between February 2011 and February 2014. Manuscripts were categorised into three groups: a "compliant" group of manuscripts using only VARC-defined endpoints, a "non-compliant" group of manu scripts with only non-VARC-defined endpoints, and a "mixed compliant" group of manuscripts with both VARC- and non-VARC-defined endpoints. Multivariate analyses were performed to identify predictors of VARC use. Among 5,023 published manuscripts, 498 were included in the final analysis. At least one VARC definition was used in 275 (54%), while 223 (43%) did not use any VARC definitions. After publication of the first VARC manuscript (VARC-1, January 2011), VARC use increased from 31% (n=15) at six months to 69% (n=84) at 36 months. Following the publication of VARC-2 (October 2012), VARC-1 use declined (from 58% [n=47] to 36% [n=24]), while VARC-2 use increased from 4% (n=3) at six months to 35% (n=23) at 18 months. Of the manuscripts using VARC, 49 (10%) were classified as compliant and 226 (46%) as mixed compliant. The following endpoints were more often defined using VARC vs. non-VARC: myocardial infarction (64% vs. 36%); stroke (56% vs. 44%); bleeding (79% vs. 21%); vascular complications (70% vs. 30%); acute kidney injury (63% vs. 37%); reintervention (67% vs. 33%); and composite endpoints (52% vs. 48%). Mortality, valve dysfunction, TAVI-related complications, and quality of life were more often defined using non-VARC criteria. CONCLUSIONS Implementation of VARC criteria in peer-reviewed manuscripts has increased over time. There remain, however, a considerable number (43%) of publications that do not report outcomes according to VARC. These data will inform the future development of VARC criteria