Have a deep view into what people are curious about.

🔗 Automobiles 🔗 Cycling

The Twike (a portmanteau of the words twin and bike) is a human-electric hybrid vehicle (HEHV) designed to carry two passengers and cargo. Essentially a velomobile with an electrical hybrid engine, it can be driven in electric-only mode or electric + pedal power mode. Pedaling warms the user, making electric heating in winter unnecessary, extends the range of the vehicle but does not substantially add to the vehicle's top speed.

Constructed of lightweight materials such as aluminium (frame) and plastic (shell), the 246 kg (542 lb) (unladen, varying with battery weight) tricycle vehicle first used NiCd batteries, later Li-Mn, LiFePO₄ and LiIon. Typically ranges reach from 50 to over 500 km depending on battery size, type, status on one side and speed and altitude profile and load on the other. Energy is reclaimed while driving through regenerative braking, and load is removed from the electric system by use of the pedalling system which transfers its input directly to the drivetrain (i.e., both systems operate in parallel, not in series).

🔗 Birds

Brood parasites are organisms that rely on others to raise their young. The strategy appears among birds, insects and fish. The brood parasite manipulates a host, either of the same or of another species, to raise its young as if it were its own, using brood mimicry, for example by having eggs that resemble the host's (egg mimicry).

Brood parasitism relieves the parasitic parents from the investment of rearing young or building nests for the young, enabling them to spend more time on other activities such as foraging and producing further offspring. Bird parasite species mitigate the risk of egg loss by distributing eggs amongst a number of different hosts. As this behaviour damages the host, it often results in an evolutionary arms race between parasite and host as the pair of species coevolve.

The strength of defenses and counter-adaptation rely on the host/parasitic species' ability to evolve; some host species have very strong rejection defenses resulting in the parasitic species evolving to have very close mimicry. In other species, hosts do not show rejection defenses and as a result, the parasitic species will show no evolved trait (example: egg mimicry).

🔗 Mathematics 🔗 Germany 🔗 Germany/Prussia

The Seven Bridges of Königsberg is a historically notable problem in mathematics. Its negative resolution by Leonhard Euler in 1736 laid the foundations of graph theory and prefigured the idea of topology.

The city of Königsberg in Prussia (now Kaliningrad, Russia) was set on both sides of the Pregel River, and included two large islands—Kneiphof and Lomse—which were connected to each other, or to the two mainland portions of the city, by seven bridges. The problem was to devise a walk through the city that would cross each of those bridges once and only once.

By way of specifying the logical task unambiguously, solutions involving either

1. reaching an island or mainland bank other than via one of the bridges, or
2. accessing any bridge without crossing to its other end

are explicitly unacceptable.

Euler proved that the problem has no solution. The difficulty he faced was the development of a suitable technique of analysis, and of subsequent tests that established this assertion with mathematical rigor.

🔗 Physics 🔗 Astronomy

Przybylski's Star (pronounced or ), or HD 101065, is a rapidly oscillating Ap star at roughly 355 light-years (109 parsecs) from the Sun in the southern constellation of Centaurus.

🔗 Women's History 🔗 Gender Studies 🔗 Albania 🔗 LGBTQ+ studies

A sworn virgin is a traditional gender variant or third gender social role in certain Balkan cultures, consisting of people who are assigned female at birth but take a vow of chastity and live the rest of their lives socially recognized as men. The practice is most common in patriarchal northern Albania, Kosovo and Montenegro, where burrnesha are recognized under the tribal Kanun law, but also exists, or has existed, to a lesser extent in other parts of the western Balkans, including Bosnia, Dalmatia (Croatia), Serbia and North Macedonia.

In times when women had a prescribed role, burrnesha gave up their preexisting sexual, reproductive and social identities to acquire the same freedoms as men. They could dress as men, be head of the household, move freely in social situations, and take work traditionally open only to men. National Geographic's Taboo estimated in 2002 that there were fewer than 102 Albanian sworn virgins left. As of 2022, while there were no exact figures, twelve burrnesha were estimated to remain in Northern Albania and Kosovo.

🔗 Mathematics

In number theory, Mills' constant is defined as the smallest positive real number A such that the floor function of the double exponential function

${\displaystyle \lfloor A^{3^{n}}\rfloor }$

is a prime number, for all natural numbers n. This constant is named after William H. Mills who proved in 1947 the existence of A based on results of Guido Hoheisel and Albert Ingham on the prime gaps. Its value is unknown, but if the Riemann hypothesis is true, it is approximately 1.3063778838630806904686144926... (sequence A051021 in the OEIS).

🔗 Energy 🔗 Engineering

A heat pipe is a heat-transfer device that employs phase transition to transfer heat between two solid interfaces.

At the hot interface of a heat pipe, a volatile liquid in contact with a thermally conductive solid surface turns into a vapor by absorbing heat from that surface. The vapor then travels along the heat pipe to the cold interface and condenses back into a liquid, releasing the latent heat. The liquid then returns to the hot interface through capillary action, centrifugal force, or gravity and the cycle repeats.

Due to the very high heat transfer coefficients for boiling and condensation, heat pipes are highly effective thermal conductors. The effective thermal conductivity varies with heat pipe length and can approach 100 kW/(m⋅K) for long heat pipes, in comparison with approximately 0.4 kW/(m⋅K) for copper.

Modern CPU heat pipes are typically made of copper and use water as the working fluid. They are common in many consumer electronics like desktops, laptops, tablets, and high-end smartphones.

🔗 Spaceflight 🔗 Physics 🔗 Systems 🔗 Systems/Dynamical systems

The Interplanetary Transport Network (ITN) is a collection of gravitationally determined pathways through the Solar System that require very little energy for an object to follow. The ITN makes particular use of Lagrange points as locations where trajectories through space are redirected using little or no energy. These points have the peculiar property of allowing objects to orbit around them, despite lacking an object to orbit. While it would use little energy, transport along the network would take a long time.

🔗 Anthroponymy 🔗 Sweden

The naming law in Sweden (Swedish: lag om personnamn) is a Swedish law which requires approval of the government agency for names to be given to Swedish children. The parents must submit the proposed name of a child within three months of birth. The current law was enacted in 2017, replacing a 1982 law. The Swedish Tax Agency administers the registration of names in Sweden. The law has been revised since originally enacted; in 1983, it was made possible for men to adopt their wife's or partner's name, as well as for women to adopt their husband's name.

The 1982 law states, in part: "First names shall not be approved if they can cause offense or can be supposed to cause discomfort for the one using it, or names which for some obvious reason are not suitable as a first name" (§ 34). This text applies both when parents name their children and when an adult wants to change their own name. When changing a name, the first change is free of charge as long as at least one of the names given at birth is kept, and such a change is only allowed once per person. Further name changes require fee payment. The law states nothing about registering which name is used on a daily basis, but the tax authority can register that if requested.

🔗 Korea 🔗 Physics 🔗 Chemicals 🔗 Electrical engineering 🔗 Materials

LK-99 is a proposed ambient pressure and room-temperature superconductor with a gray‒black appearance.^: 8 LK-99 has a hexagonal structure slightly modified from lead‒apatite and is claimed to function as a superconductor below 400 K (127 °C; 260 °F).^: 1 The material was investigated by a team of Sukbae Lee et al. from the Korea Institute of Science and Technology (KIST).^: 1 As of 26 July 2023 the discovery of LK-99 has not been peer reviewed or independently replicated.

The chemical composition of LK-99 is approximately Pb₉Cu(PO₄)₆O such that—compared to pure lead-apatite (Pb₁₀(PO₄)₆O)^: 5—approximately one quarter of Pb(2) ions are replaced by Cu(II) ions.^: 9 This partial replacement of Pb²⁺ ions (measuring 133 picometre) with Cu²⁺ ions (measuring 87 picometre) is said to cause a 0.48% reduction in volume, creating internal stress inside the material.^: 8

The internal stress is claimed to cause a heterojunction quantum well between the Pb(1) and oxygen within the phosphate ([PO₄]³⁻) generating a superconducting quantum well (SQW).^: 10 Lee et al claim to show LK-99 exhibits a response to a magnetic field (Meissner effect) when chemical vapor deposition is used to apply LK-99 to a non-magnetic copper sample.^: 4 Pure lead-apatite is an insulator, but Lee et al claim copper-doped lead-apatite forming LK-99 is a superconductor, or at higher temperatures, a metal.^: 5