BR
Bertrand Arthur William Russell, 3rd Earl Russell (18 May 1872 – 2 February 1970) was a British philosopher, logician, mathematician, and social critic renowned for his foundational work in analytic philosophy and mathematical logic.[1] He co-authored Principia Mathematica (1910–1913) with Alfred North Whitehead, a monumental effort to derive all of mathematics from logical axioms, addressing paradoxes like the set-theoretic issues that bear his name.[2] Russell received the Nobel Prize in Literature in 1950 "in recognition of his varied and significant writings in which he champions humanitarian ideals and freedom of thought."[3] A committed pacifist, he was imprisoned in 1918 for opposing conscription during World War I, and later co-initiated the Russell–Einstein Manifesto in 1955, warning of the existential risks posed by nuclear weapons and advocating for their abolition.[4][5] His prolific output spanned epistemology, ethics, and politics, emphasizing empirical inquiry and skepticism toward dogma, though his outspoken views often provoked controversy, including academic dismissals and public backlash for his critiques of religion and advocacy for rational secularism.[1]Physical sciences
Bromine
Bromine is a chemical element with the symbol Br and atomic number 35.[6] It belongs to the halogen group (Group 17) in the periodic table and exists as a dense, volatile, reddish-brown liquid at standard temperature and pressure, readily forming a pungent, similarly colored vapor.[7] The element's atomic mass is 79.904 u, and it has an electron configuration of [Ar] 3d¹⁰ 4s² 4p⁵, making it highly electronegative with a Pauling electronegativity of 2.96.[7] Bromine is less reactive than fluorine or chlorine but more reactive than iodine, readily forming bromide ions (Br⁻) in compounds and exhibiting intermediate oxidizing power among halogens.[8] Bromine was independently discovered in 1826 by French chemist Antoine-Jérôme Balard, who isolated it from the bittern (concentrated residue) of saltwater from Montpellier, France, and by German chemist Carl Jacob Löwig from similar brines.[9] Balard named it "bromine" from the Greek brômos, meaning "stench," due to its strong odor.[7] The element occurs naturally as bromide ions in seawater at concentrations of about 65 mg/L and in concentrated brines such as those in the Dead Sea, where it constitutes up to 5 g/L; it is the 46th most abundant element in Earth's crust at roughly 2.5 ppm.[10] Commercially, bromine is produced by treating bromide-rich brines with chlorine gas to displace and liberate elemental bromine, followed by steam distillation and purification; global production exceeds 300,000 metric tons annually, primarily from Israel, the United States, and China.[11] Key physical properties include a density of 3.10 g/cm³ at 20°C, a melting point of -7.2°C, and a boiling point of 58.8°C, making it the only nonmetallic element that is liquid at near-room temperature.[7] Chemically, bromine reacts vigorously with metals to form bromides, displaces iodine from iodides, and participates in addition reactions with unsaturated hydrocarbons, but it requires catalysts or light for reactions with alkanes unlike chlorine.[8] Bromine compounds find applications in flame retardants (e.g., polybrominated diphenyl ethers, though some face regulatory scrutiny), water disinfection (as hypobromous acid), pharmaceuticals (e.g., sedatives like barbital), and oil drilling fluids; it also serves in analytical chemistry for bromination tests.[11] Bromine is highly toxic and corrosive, causing severe burns on skin contact, respiratory irritation, and pulmonary edema upon inhalation; its permissible exposure limit is 0.1 ppm over 8 hours.[12] Acute exposure leads to symptoms like coughing, headache, and lacrimation, while chronic bromism from bromide accumulation can impair cognition and cause skin rashes.[13] Elemental bromine reacts explosively with some reducing agents and emits toxic fumes when heated or mixed with water.[14] Despite its hazards, bromine has no known essential biological role in humans, though bromide ions occur trace-level in tissues.[10]Computing and information technology
Line break element (
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The <br> element is a void element in HTML that inserts a line break in text content, equivalent to a carriage return in rendering.[15] It must be used solely for semantic line breaks inherent to the content, such as in poems, song lyrics, or postal addresses, rather than for visual layout purposes, which should instead employ CSS properties like display: block or margins.[15] As a phrasing content element, it can appear within parent elements like <p>, <li>, or <div>, but consecutive <br> elements or misuse for spacing violates HTML5 conformance and may lead to inconsistent rendering across browsers.[15]
Introduced in early HTML specifications dating to the 1990s, the <br> element originated as a simple mechanism to override default word wrapping in inline text flows, predating widespread CSS adoption for formatting control. In HTML 4.01, it was classified under text-level elements with optional attributes like clear for image alignment, though such attributes are obsolete in HTML5. The WHATWG HTML Living Standard, maintained since 2011 as the de facto reference for modern implementations, explicitly deprecates non-semantic uses to promote accessible, maintainable markup; for instance, browsers like Chrome and Firefox render <br> as a single newline without collapsing multiples, but screen readers interpret it as a structural pause.[15]
No attributes are required or recommended for the <br> element in contemporary HTML; the self-closing form <br> is valid and preferred over <br /> in HTML5 serialization, though both parse identically in tolerant parsers. Overuse has drawn criticism for hindering responsive design, as evidenced by web standards bodies advocating CSS alternatives like white-space: pre-line for preserving breaks without markup proliferation. Empirical browser compatibility data confirms universal support since Internet Explorer 3 (1996), with no significant rendering variances in standards-compliant modes.