Archaea constitute a domain of single-celled organisms. These microorganisms are therefore prokaryotes. Archaea were classified as bacteria, receiving the name archaebacteria, but this classification is outmoded, they have been renamed to clarify that archaea are not only not bacteria, but are more related to eukaryotes than to real bacteria. Archaeal cells have unique properties separating them from the other two domains and Eukaryota. Archaea are further divided into multiple recognized phyla. Classification is difficult because most have not been isolated in the laboratory and have only been detected by analysis of their nucleic acids in samples from their environment. Archaea and bacteria are similar in size and shape, although a few archaea have different shapes, such as the flat and square cells of Haloquadratum walsbyi. Despite this morphological similarity to bacteria, archaea possess genes and several metabolic pathways that are more related to those of eukaryotes, notably for the enzymes involved in transcription and translation.

Other aspects of archaeal biochemistry are unique, such as their reliance on ether lipids in their cell membranes, including archaeols. Archaea use more energy sources than eukaryotes: these range from organic compounds, such as sugars, to ammonia, metal ions or hydrogen gas. Salt-tolerant archaea use sunlight as an energy source, other species of archaea fix carbon, but unlike plants and cyanobacteria, no known species of archaea does both. Archaea reproduce asexually by budding; the first observed archaea were extremophiles, living in extreme environments, such as hot springs and salt lakes with no other organisms. Improved detection tools led to the discovery of archaea in every habitat, including soil and marshlands. Archaea are numerous in the oceans, the archaea in plankton may be one of the most abundant groups of organisms on the planet. Archaea are a major part of Earth's life, they are part of the microbiota of all organisms. In the human microbiota, they are important in the gut, on the skin.

They may play roles in the nitrogen cycle. No clear examples of archaeal pathogens or parasites are known. Instead they are mutualists or commensals, such as the methanogens that inhabit the gastrointestinal tract in humans and ruminants, where their vast numbers aid digestion. Methanogens are used in biogas production and sewage treatment, biotechnology exploits enzymes from extremophile archaea that can endure high temperatures and organic solvents. For much of the 20th century, prokaryotes were regarded as a single group of organisms and classified based on their biochemistry and metabolism. Microbiologists tried to classify microorganisms based on the structures of their cell walls, their shapes, the substances they consume. In 1965, Emile Zuckerkandl and Linus Pauling instead proposed using the sequences of the genes in different prokaryotes to work out how they are related to each other; this phylogenetic approach is the main method used today. Archaea – at that time only the methanogens were known – were first classified separately from bacteria in 1977 by Carl Woese and George E. Fox based on their ribosomal RNA genes.

They called these groups the Urkingdoms of Archaebacteria and Eubacteria, though other researchers treated them as kingdoms or subkingdoms. Woese and Fox gave the first evidence for Archaebacteria as a separate "line of descent": 1. Lack of peptidoglycan in their cell walls, 2. Two unusual coenzymes, 3. Results of 16S ribosomal RNA gene sequencing. To emphasize this difference, Otto Kandler and Mark Wheelis proposed reclassifying organisms into three natural domains known as the three-domain system: the Eukarya, the Bacteria and the Archaea, in what is now known as "The Woesian Revolution"; the word archaea comes from the Ancient Greek ἀρχαῖα, meaning "ancient things", as the first representatives of the domain Archaea were methanogens and it was assumed that their metabolism reflected Earth's primitive atmosphere and the organisms' antiquity, but as new habitats were studied, more organisms were discovered. Extreme halophilic and hyperthermophilic microbes were included in Archaea. For a long time, archaea were seen as extremophiles that only exist in extreme habitats such as hot springs and salt lakes, but by the end of the 20th century, archaea had been identified in non-extreme environments as well.

Today, they are known to be a large and diverse group of organisms abundantly distributed throughout nature. This new appreciation of the importance and ubiquity of archaea came from using polymerase chain reaction to detect prokaryotes from environmental samples by multiplying their ribosomal genes; this allows the detection and identification of organisms that have not been cultured in the laboratory. The classification of archaea, of prokaryotes in general, is a moving and contentious field. Current classification systems aim to organize archaea into groups of organisms that share structural features and common ancestors; these classifications rely on the use of the sequence of ribosomal RNA genes to reveal relationships between organisms. Most of the culturable and well-investigated species of archaea are members of two main phyla, the Euryarchaeota and Crenarchaeota. Other groups have been tentatively created, like the peculiar species Nanoarchaeum equitans, dis

Margherita Bevignani was an Italian operatic soprano, best known for being the first singer to record the entire role of Violetta in Giuseppe Verdi's opera La traviata in 1915. Information is lacking concerning Bevignani's place of her early years, she was born in 1887 and studied singing with a certain teacher Perilli. She made her debut in 1909 at Politeama Garibaldi in Treviso as Micaela in Bizet's Carmen. Subsequently, she was invited to many Italian provincial stages, such as the Teatro Petruzzelli in Bari and the Teatro Massimo Bellini in Catania. In 1910 she made several guest appearances in a number of opera houses of Latin America, including the Theatro Municipal in Rio de Janeiro, where she sang Musetta in Puccini's La bohème and Gilda in Rigoletto. In 1911 she performed the role of Marguerite de Valois in Giacomo Meyerbeer's Les Huguenots at the Teatro Donizetti in Bergamo under the direction of Gino Marinuzzi. In 1912 Bevignani arrived in Milan, where she sang Amina in Bellini's La sonnambula at the Teatro dal Verme, though never appeared at La Scala.

In the same year she toured London, despite never managing to sing at The Royal Opera House, she performed Nedda in Leoncavallo's Pagliacci at the Coliseum Theatre. In 1914-1916 Bevignani was invited to the Netherlands, where she was praised for her Violetta in La traviata as well as Norina in Gaetano Donizetti's Don Pasquale. Italy's entrance into the First World War forced the singer's stay in the Netherlands, where she gave successful performances as Violetta, Rosina in Rossini's Il barbiere di Siviglia and Lucia di Lammermoor in Donizetti's opera of the same title. After returning to Italy in 1918, Bevignani was struck by a fierce attack of pulmonary tuberculosis which put an end to her career, her last performance was La traviata at the Royal Theatre Carré in Amsterdam where she sang Violetta. Margherita Bevignani died in Milan in March 1921. Though Margherita Bevignani did not achieve any worldwide recognition and never managed to sing at any of the world's principal opera houses, the name of this singer is significant.

She sang Violetta in the first complete Italian recording of La traviata in 1915 with Franco Tumminello and Ernesto Badini as partners, made by HMV in Milan with the forces of La Scala under the direction of Carlo Sabajno. It shows Bevignani as a coloratura soprano. In addition, Bevignani can be heard on a number of separate recordings made for the Favorite company, including extended excerpts from Gounod's Faust and duets by Verdi, Donizetti, Rossini and Massenet

The 15767 / 68 Siliguri Junction - Alipurduar Junction Intercity Express is an Express train belonging to Indian Railways Northeast Frontier Railway zone that runs between Siliguri Junction and Alipurduar Junction in India. It operates as train number 15767 from Siliguri Junction to Alipurduar Junction and as train number 15768 in the reverse direction serving the states of West Bengal; the 15767 / 68 Siliguri Junction - Alipurduar Junction Intercity Express has nine general unreserved & two SLR coaches. It does not carry a pantry car coach; as is customary with most train services in India, coach composition may be amended at the discretion of Indian Railways depending on demand. The 15767 Siliguri Junction - Alipurduar Junction Intercity Express covers the distance of 161 km in 4 hours 45 mins & in 4 hours 00 mins as the 15768 Alipurduar Junction - Siliguri Junction Intercity Express; as the average speed of the train is lower than 55 km/h, as per railway rules, its fare doesn't include a Superfast surcharge.

The 15767 / 68 Siliguri Junction - Alipurduar Junction Intercity Express runs from Siliguri Junction via Oodlabari New Mal Junction Chalsa Nagrakata Banarhat Binnaguri Dalgaon Madarihat Hasimara Hamiltonganj Kalchini Rajabhat Khawa to Alipurduar Junction in West Bengal. As the route is going to electrification, a Malda Town based WDM-3D diesel locomotive pulls the train to its destination. 15767 Intercity Express at India Rail Info 15768 Intercity Express at India Rail Info