Modelling and experiments of self-reflectivity under femtosecond ablation conditions

We present a numerical model which describes the propagation of a single femtosecond laser pulse in a medium of which the optical properties dynamically change within the duration of the pulse. We use a Finite Difference Time Domain (FDTD) method to solve the Maxwell's equations coupled to equations describing the changes in the material properties. We use the model to simulate the self-reflectivity of strongly focused femtosecond laser pulses on silicon and gold under laser ablation condition. We compare the simulations to experimental results and find excellent agreement.Comment: 11 pages, 8 figure

Primary radiotherapy in progressive optic nerve sheath meningiomas: a long-term follow-up study

Background/aims: To report the outcome of primary radiotherapy in patients with progressive optic nerve sheath meningioma (ONSM). Methods: The clinical records of all patients were reviewed in a retrospective, observational, multicentre study. Results: Thirty-four consecutive patients were included. Twenty-six women and eight men received conventional or stereotactic fractionated radiotherapy, and were followed for a median 58 (range 51–156) months. Fourteen eyes (41%) showed improved visual acuity of at least two lines on the Snellen chart. In 17 (50%) eyes, the vision stabilised, while deterioration was noted in three eyes (9%). The visual outcome was not associated with age at the time of radiotherapy (p=0.83), sex (p=0.43), visual acuity at the time of presentation (p=0.22) or type of radiotherapy (p=0.35). Optic disc swelling was associated with improved visual acuity (p<0.01) and 4/11 patients with optic atrophy also showed improvement. Long-term complications were dry eyes in five patients, cataracts in three, and mild radiation retinopathy in four. Conclusion: Primary radiotherapy for patients with ONSM is associated with long-term improvement of visual acuity and few adverse effects.Peerooz Saeed, Leo Blank, Dinesh Selva, John G. Wolbers, Peter J.C.M. Nowak, Ronald B. Geskus, Ezekiel Weis, Maarten P. Mourits, Jack Rootma

Testing of High Voltage Surge Protection Devices for Use in Liquid Argon TPC Detectors

In this paper we demonstrate the capability of high voltage varistors and gas discharge tube arrestors for use as surge protection devices in liquid argon time projection chamber detectors. The insulating and clamping behavior of each type of device is characterized in air (room temperature), and liquid argon (90~K), and their robustness under high voltage and high energy surges in cryogenic conditions is verified. The protection of vulnerable components in liquid argon during a 150 kV high voltage discharge is also demonstrated. Each device is tested for argon contamination and light emission effects, and both are constrained to levels where no significant impact upon liquid argon time projection chamber functionality is expected. Both devices investigated are shown to be suitable for HV surge protection applications in cryogenic detectors.Comment: 22 pages, 18 figures v2: reduced file size for journal submissio

In sturing blijven in dynamische operaties: Het deficit van ‘command & control’?

NWO016.Veni.195.121Security and Global Affair

Destination choices of international students in the Netherlands:A meso‐level analysis of higher education institutions and cities

This study quantitatively investigates enrolments of international students using data that contains nearly every student in the Netherlands for the years 2016–2019. Using this data, we are able to perform a meso-level analysis where we could investigate the characteristics of higher education institutions (HEIs) and cities in international student mobility. This research contributes to the literature by studying variation between HEIs and by focusing on actual enrolments instead of relying on survey results. Such meso-level studies have thus far been very rare, especially on this scale. Although there are commonalities between types of degrees, we find mixed results for academic and city characteristics, and it appears that academic factors are more important for master students while for bachelor students city characteristics have stronger effects. The effect of having already existing stocks of international students appears to be important for all types of degrees. Aside from differences between bachelor and master students, our findings also suggest that HEIs might directly influence international student flows as this would explain some of our results. Although this study only focuses on the Netherlands, it opens up many avenues for future comparative research on the destination choices of international students and the role of HEIs

Codifying a crisis: progressing from information sharing to distributed decision‐making

A key challenge in crisis management is maintaining an adequate information position to support coherent decision‐making between a range of actors. Such distributed decision‐making is often supported by a common operational picture that not only conveys factual information but also attempts to codify a dynamic and vibrant crisis management process. In this paper, we explain why it is so difficult to move from information sharing towards support for distributed decision‐making. We argue that two key processes need to be considered: supporting both the translation of meaning and the transformation of interests between those on the front line and those in the remote response network. Our analysis compares the information‐sharing processes in three large‐scale emergency response operations in the Netherlands. Results indicate that on several occasions the collaborative decision‐making process was hampered because actors limited themselves to factual information exchange. The decision‐making process only succeeds when actors take steps to resolve their varying interpretations and interests. This insight offers important lessons for improving information management doctrines and for supporting distributed decision‐making processes.NWO016.Veni.195.121Security and Global Affair

To the edge and beyond: How fast-response organizations adapt in rapidly changing crisis situations

Fast-response organizations excel in mounting swift and coordinated responses to unexpected events. There are a multitude of conflicting explanations why these organizations excel. These range from acknowledging the strengths of centralized command and control structures, towards stressing the importance of decentralized, improvised action. Though this dichotomy is derived from studies offering either structure or action-based explanations, we were able to reconcile these insights by looking into the process of how fast-responders organize themselves during an unfolding crisis. We analyzed 15 high-speed police pursuits crossing multiple administrative units and jurisdictions, and interviewed and observed officers at work in multiple operations centers, police cars, and helicopters. Our analysis uncovered that fast-responders regularly transition between designed, frontline, and partitioned modes of organizing, each characterized by practices that shape command, allocation, and information sharing. Success and failure are rooted in the ability of the responders to adapt their mode of organizing by tacking back and forth between these practices. Based on our findings, we constructed a process model that provides a deeper understanding of fast-response organizing that informs future studies on organizing in extreme contexts.NWO016.Veni.195.121Security and Global Affair