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Concept: Christiaan Huygens


The synchronization of two pendulum clocks hanging from a wall was first observed by Huygens during the XVII century. This type of synchronization is observed in other areas, and is fundamentally different from the problem of two clocks hanging from a moveable base. We present a model explaining the phase opposition synchronization of two pendulum clocks in those conditions. The predicted behaviour is observed experimentally, validating the model.

Concepts: Scientific method, Hypothesis, Das Model, Base, Problem of evil, Pendulum clock, Christiaan Huygens


This paper introduces a modern version of the classical Huygens' experiment on synchronization of pendulum clocks. The version presented here consists of two monumental pendulum clocks-ad hoc designed and fabricated-which are coupled through a wooden structure. It is demonstrated that the coupled clocks exhibit ‘sympathetic’ motion, i.e. the pendula of the clocks oscillate in consonance and in the same direction. Interestingly, when the clocks are synchronized, the common oscillation frequency decreases, i.e. the clocks become slow and inaccurate. In order to rigorously explain these findings, a mathematical model for the coupled clocks is obtained by using well-established physical and mechanical laws and likewise, a theoretical analysis is conducted. Ultimately, the sympathy of two monumental pendulum clocks, interacting via a flexible coupling structure, is experimentally, numerically, and analytically demonstrated.

Concepts: Scientific method, Science, Theory, Harmonic oscillator, Simple harmonic motion, Pendulum clock, Christiaan Huygens, Escapement


Early prediction of admission has the potential to reduce length of stay in the ED. The aim of this study is to create a computerised tool to predict admission probability.

Concepts: Prostitution in the Netherlands, Christiaan Huygens


The anatomical collection of the Anatomical Museum of Leiden University Medical Center (historically referred to as Museum Anatomicum Academiae Lugduno-Batavae) houses and maintains more than 13,000 unique anatomical, pathological and zoological specimens, and include the oldest teratological specimens of The Netherlands. Throughout four centuries hundreds of teratological specimens were acquired by more than a dozen collectors. Due to the rich history of this vast collection, teratological specimens can be investigated in a unique retrospective sight going back almost four centuries. The entire 19th century collection was described in full detail by Eduard Sandifort (1742-1814) and his son Gerard Sandifort (1779-1848). Efforts were made to re-describe, re-diagnose and re-categorize all present human teratological specimens, and to match them with historical descriptions. In the extant collection a total of 642 human teratological specimens were identified, including exceptional conditions such as faciocranioschisis and conjoined twins discordant for cyclopia, and sirenomelia. Both father and son Sandifort differed in their opinion regarding the causative explanation of congenital anomalies. Whereas, their contemporaries Wouter Van Doeveren (1730-1783) and Andreas Bonn (1738-1817) both presented an interesting view on how congenital anomalies were perceived and explained during the 18th and 19th centuries; the golden age of descriptive teratology. Although this enormous collection is almost 400 years old, it still impresses scientists, (bio)medical students, and laymen visiting and exploring the collections of the Museum Anatomicum in Leiden, The Netherlands.

Concepts: Biology, Centuries, Congenital disorders, 19th century, The Hague, Leiden University Library, Beatrix of the Netherlands, Christiaan Huygens


Christiaan Huygens (1629-1695) was a Dutch mathematician, physicist, and astronomer. He became well-known as inventor of the pendulum clock and described light as a wave phenomenon. He became Fellow of the Royal Society (London) and member of the Académie des Sciences (Paris). From the correspondence with family members and famous scientists, we learn that he suffered from frequent headaches.

Concepts: Netherlands, Scientist, Robert Hooke, Pendulum, Horology, Pendulum clock, Christiaan Huygens


Coxiella burnetii causes Q fever, a zoonosis, which has acute and chronic manifestations. From 2007 to 2010, the Netherlands experienced a large Q fever outbreak, which has offered a unique opportunity to analyze chronic Q fever cases. In an observational cohort study, base-line characteristics, clinical characteristics, as well as mortality of patients with proven, probable or possible chronic Q fever in the Netherlands were analyzed. In total, 284 chronic Q fever patients were identified, of which 151 (53.7%) had proven, 64 (22.5%) probable and 69 (24.3%) possible chronic Q fever. Among proven and probable chronic Q fever patients, vascular infection focus (56.7%) was more prevalent than endocarditis (34.9%). An acute Q fever episode could be recalled by 27.0% of patients. All-cause mortality was 19.1%, while chronic Q fever-related mortality was 13.0%; 9.3% among endocarditis patients and 18.0% among vascular chronic Q fever patients. Increasing age (p-values 0.004, 0.010), proven chronic Q fever (p-values 0.020, 0.002), vascular chronic Q fever (p-values 0.024, 0.005), acute presentation with chronic Q fever (p-values 0.002, <0.001) and surgical treatment of chronic Q fever (p-values 0.025, <0.001) were significantly associated with all-cause mortality and chronic Q fever-related mortality, respectively.

Concepts: Cohort study, Epidemiology, Coxiella burnetii, Q fever, Netherlands, Dutch people, Dutch language, Christiaan Huygens