# Melatonin 褪黑素

Melatonin is a hormone primarily released by the pineal gland at night, and has long been associated with control of the sleep–wake cycle.

In vertebrates, melatonin is involved in synchronizing circadian rhythms, including sleep–wake timing and blood pressure regulation, and in control of seasonal rhythmicity including reproduction, fattening, moulting and hibernation. Many of its effects are through activation of the melatonin receptors, while others are due to its role as an antioxidant. In plants, it functions to defend against oxidative stress. It is also present in various foods.

In animals, melatonin plays an important role in the regulation of sleep–wake cycles. Human infants’ melatonin levels become regular in about the third month after birth, with the highest levels measured between midnight and 8:00 am. Human melatonin production decreases as a person ages. Also, as children become teenagers, the nightly schedule of melatonin release is delayed, leading to later sleeping and waking times.

Melatonin occurs at high concentrations within mitochondrial fluid which greatly exceed the plasma concentration of melatonin. Due to its capacity for free radical scavenging, indirect effects on the expression of antioxidant enzymes, and its significant concentrations within mitochondria, a number of authors have indicated that melatonin has an important physiological function as a mitochondrial antioxidant.

While it is known that melatonin interacts with the immune system, the details of those interactions are unclear. An antiinflammatory effect seems to be the most relevant. There have been few trials designed to judge the effectiveness of melatonin in disease treatment. Most existing data are based on small, incomplete trials. Any positive immunological effect is thought to be the result of melatonin acting on high-affinity receptors (MT1 and MT2) expressed in immunocompetent cells. In preclinical studies, melatonin may enhance cytokine production, and by doing this, counteract acquired immunodeficiences. Some studies also suggest that melatonin might be useful fighting infectious disease including viral, such as HIV, and bacterial infections, and potentially in the treatment of cancer.

# Civil Aviation 民航

Civil aviation is one of two major categories of flying, representing all non-military and non-state aviation, both private and commercial. Most of the countries in the world are members of the International Civil Aviation Organization (ICAO) and work together to establish common standards and recommended practices for civil aviation through that agency. Civil aviation includes three major categories: Commercial air transport, including scheduled and non-scheduled passenger and cargo flights Aerial work, in which an aircraft is used for specialized services such as agriculture, photography, surveying, search and rescue, etc. General aviation (GA), including all other civil flights, private or commercial. Commercial aviation is the part of civil aviation that involves operating aircraft for remuneration or hire, as opposed to private aviation. Flight or Airline is a scheduled trip by plane between designated airports. Civil aviation authoritiesThe Convention on International Civil Aviation (the “Chicago Convention”) was originally established in 1944; it states that signatories should collectively work to harmonize and standardize the use of airspace for safety, efficiency and regularity of air transport. Each signatory country, of which there are at least 193, has a civil aviation authority (such as the FAA in the United States) to oversee the following areas of civil aviation: Personnel licensing — regulating the basic training and issuance of licenses and certificates. Flight operations — carrying out safety oversight of commercial operators. Airworthiness — issuing certificates of registration and certificates of airworthiness to civil aircraft, and overseeing the safety of aircraft maintenance organizations. Aerodromes — designing and constructing aerodrome facilities. Air traffic services — managing the traffic inside of a country’s airspace.

# Rocket Equation 火箭方程

Rocket equation is a mathematical equation that describes the motion of vehicles that follow the basic principle of a rocket: a device that can apply acceleration to itself using thrust by expelling part of its mass with high velocity can thereby move due to the conservation of momentum. Ideal Rocket Equation$$\Delta v=v_{\mathrm{e}} \ln \frac{m_{0}}{m_{f}}=I_{\mathrm{sp}} g_{0} \ln \frac{m_{0}}{m_{f}}$$ where: $\Delta v$ is delta-v – the maximum change of velocity of the vehicle (with no external forces acting). ${m_{0}}$ is the initial total mass, including propellant, a.k.a. wet mass. ${m_{f}}$ is the final total mass without propellant, a.k.a. dry mass. $v_{\mathrm{e}} = I_{\mathrm{sp}} g_{0}$ is the effective exhaust velocity, where: $I_{\mathrm{sp}}$ is the specific impulse in dimension of time. $g_{0}$ is standard gravity. $\ln$ is is the natural logarithm function. Given the effective exhaust velocity $v_{\mathrm{e}}$ (determined by a rocket motor’s design), a desired delta-v (for example, escape velocity), and a given dry mass ${m_{f}}$, the equation can be used to find the required wet mass ${m_{0}} - {m_{f}}$ : $$m_{0}=m_{f} e^{\frac{\Delta v}{v_{\mathrm{e}}}}$$ So the necessary wet mass grows exponentially with the desired delta-v, as illustrated in the chart. Terms of the equationDelta-vDelta-v (literally “change in velocity”), symbolised as ${\Delta v}$ and pronounced delta-vee, as used in spacecraft flight dynamics, is a measure of the impulse that is needed to perform a maneuver such as launching from, or landing on a planet or moon, or an in-space orbital maneuver. It is a scalar that has the units of speed. As used in this context, it is not the same as the physical change in velocity of the vehicle. Delta-v is produced by reaction engines, such as rocket engines and is proportional to the thrust per unit mass, and burn time, and is used to determine the mass of propellant required for the given manoeuvre through the rocket equation. For multiple manoeuvres, delta-v sums linearly. For interplanetary missions delta-v is often plotted on a porkchop plot which displays the required mission delta-v as a function of launch date.

# Ai 人工智能

Artificial super intelligence is humanity’s last invention, no reason to be scared. Let’s take a journey into the future and explore how Ai develops and changes humanity paving the way for robots that are too fast for humans to see in 10 years time, for the creation of Ai-free zones in 60 years. For energy being rationed for humans to power the super AIs in 90 years, and for human consciousness to be transmitted into space as data in 200 years time. 2028People are having natural conversations with artificial intelligence. Google’s Lambda allows humans to talk to expert AIs on any topic starting to replace the need for online searches. Elon Musk’s Neurolink graduates from being a medical device and testing begins on increasing human intelligence. This gets the name IA (Intelligence Amplification) peripherals physical add-ons are being developed, such as zoom cameras sonar based night vision and taste modifiers that can all be connected to the brain chip. 2030Loved ones who have passed away are being turned into digital avatars. These Ai chat bots patented by Microsoft learn how to respond by studying the text audio and video conversations from when the human was alive. Ai limbs robotic arm prosthetics start to have artificial intelligence built into them, allowing the prosthetics to download new skills, such as how to play different songs on a piano or how to build things. More advanced Ai limbs are being developed that are more self-aware operating as their own entity they are able to catch a falling glass bottle before the human user is even aware that it is moved the internet of things begins to evolve into the artificial intelligence of things. Everyday objects such as coffee machines and toothbrushes that collect data, and are connected to the internet now possess Ai. A second internet begins testing dedicated to the artificial intelligence of things. Humanity tries to isolate humans and machines with separate internets. Ai Quantum Computing begins to make new discoveries calculations can be made in seconds rather than thousands of years where traditional computers were used for physics simulations, such as simulating wind tunnels quantum computing can run simulations down to an atomic and molecular level. The Quantum Ai is used to design new medicines and materials. Ai is being used to regulate news, it can understand human speech in all languages and begins working on creating a universal language. Artificial intelligence starts to take over hospitals, marking the beginnings of a new era in humanity’s mortality. Away from public view, advanced Ai is being used in military simulations, millions of strategic scenarios are played out virtually before being rolled out to dictate global politics and conflicts.

# Earthquake 地震

Quaking or shaking of the earth is a common phenomenon undoubtedly known to humans from the earliest times. Before the development of strong-motion accelerometers that can measure peak ground speed and acceleration directly, the intensity of the earth-shaking was estimated based on the observed effects, as categorized on various seismic intensity scales. Only in the last century has the source of such shaking been identified as ruptures in the Earth’s crust, with the intensity of shaking at any locality dependent not only on the local ground conditions but also on the strength or magnitude of the rupture, and on its distance. Subsequent scales (see seismic magnitude scales) have retained a key feature, where each unit represents a ten-fold difference in the amplitude of the ground shaking and a 32-fold difference in energy. Subsequent scales are also adjusted to have approximately the same numeric value within the limits of the scale. Although the mass media commonly reports earthquake magnitudes as “Richter magnitude” or “Richter scale”, standard practice by most seismological authorities is to express an earthquake’s strength on the moment magnitude scale, which is based on the actual energy released by an earthquake. Measuring and locating earthquakesSeismic waves travel through the Earth’s interior and can be recorded by seismometers at great distances. The surface wave magnitude was developed as a means to measure remote earthquakes and to improve the accuracy for larger events. The moment magnitude scale not only measures the amplitude of the shock but also takes into account the seismic moment (total rupture area, average slip of the fault, and rigidity of the rock). The Japan Meteorological Agency seismic intensity scale, the Medvedev–Sponheuer–Karnik scale, and the Mercalli intensity scale are based on the observed effects and are related to the intensity of shaking. Every tremor produces different types of seismic waves, which travel through rock with different velocities: Longitudinal P-waves (shock- or pressure waves) Transverse S-waves (both body waves) Surface waves – (Rayleigh and Love waves) Propagation velocity of the seismic waves through solid rock ranges from approx. 3 km/s (1.9 mi/s) up to 13 km/s (8.1 mi/s), depending on the density and elasticity of the medium. In the Earth’s interior, the shock- or P-waves travel much faster than the S-waves (approx. relation 1.7:1). The differences in travel time from the epicenter to the observatory are a measure of the distance and can be used to image both sources of quakes and structures within the Earth. Also, the depth of the hypocenter can be computed roughly. In the upper crust, P-waves travel in the range 2–3 km (1.2–1.9 mi) per second (or lower) in soils and unconsolidated sediments, increasing to 3–6 km (1.9–3.7 mi) per second in solid rock. In the lower crust, they travel at about 6–7 km (3.7–4.3 mi) per second; the velocity increases within the deep mantle to about 13 km (8.1 mi) per second. The velocity of S-waves ranges from 2–3 km (1.2–1.9 mi) per second in light sediments and 4–5 km (2.5–3.1 mi) per second in the Earth’s crust up to 7 km (4.3 mi) per second in the deep mantle. As a consequence, the first waves of a distant earthquake arrive at an observatory via the Earth’s mantle. On average, the kilometer distance to the earthquake is the number of seconds between the P- and S-wave times 8. Slight deviations are caused by inhomogeneities of subsurface structure. S-waves and later arriving surface waves do most of the damage compared to P-waves. P-waves squeeze and expand the material in the same direction they are traveling, whereas S-waves shake the ground up and down and back and forth. Earthquakes are not only categorized by their magnitude but also by the place where they occur. The world is divided into 754 Flinn–Engdahl regions (F-E regions), which are based on political and geographical boundaries as well as seismic activity. More active zones are divided into smaller F-E regions whereas less active zones belong to larger F-E regions. Standard reporting of earthquakes includes its magnitude, date and time of occurrence, geographic coordinates of its epicenter, depth of the epicenter, geographical region, distances to population centers, location uncertainty, several parameters that are included in USGS earthquake reports (number of stations reporting, number of observations, etc.), and a unique event ID.

# DSN 深空网络

Deep Space Network (DSN) currently consists of three deep-space communications facilities placed approximately 120 degrees apart around the Earth. They are: the Goldstone Deep Space Communications Complex (35°25′36″N 116°53′24″W) outside Barstow, California. For details of Goldstone’s contribution to the early days of space probe tracking. the Madrid Deep Space Communications Complex (40°25′53″N 4°14′53″W), 60 kilometres (37 mi) west of Madrid, Spain. the Canberra Deep Space Communication Complex (CDSCC) in the Australian Capital Territory (35°24′05″S 148°58′54″E), 40 kilometres (25 mi) southwest of Canberra, Australia near the Tidbinbilla Nature Reserve. Each facility is situated in semi-mountainous, bowl-shaped terrain to help shield against radio frequency interference. The strategic placement with nearly 120-degree separation permits constant observation of spacecraft as the Earth rotates, which helps to make the DSN the largest and most sensitive scientific telecommunications system in the world. All DSN antennas are steerable, high-gain, parabolic reflector antennas. The antennas and data delivery systems make it possible to: acquire telemetry data from spacecraft. transmit commands to spacecraft. upload software modifications to spacecraft. track spacecraft position and velocity. perform Very Long Baseline Interferometry observations. measure variations in radio waves for radio science experiments. gather science data. monitor and control the performance of the network. The DSN operates according to the standards of the Consultative Committee for Space Data Systems, as do most other deep space networks, and hence the DSN is able to interoperate with the networks of other space agencies.

# CRISPR 基因编辑

Clustered Regularly Interspaced Short Palindromic RepeatsRepetitive DNA sequences, called CRISPR, were observed in bacteria with spacer DNA sequences in between the repeats that exactly match viral sequences. It was subsequently discovered that bacteria transcribe these DNA elements to RNA upon viral infection. The RNA guides a nuclease (a protein that cleaves DNA) to the viral DNA to cut it, providing protection against the virus. The nucleases are named Cas, for CRISPR-associated. Genome editingIn 2012, researchers demonstrated that RNAs could be constructed to guide a Cas nuclease (Cas9 was the first used) to any DNA sequence. The so-called guide RNA can also be made so that it will be specific to only that one sequence, improving the chances that the DNA will be cut at that site and nowhere else in the genome. Further testing revealed that the system works quite well in all types of cells, including human cells. ImplicationsWith CRISPR/Cas, it’s easy to disrupt a targeted gene, or, if a DNA template is added to the mix, insert a new sequence at the precise spot desired. The method has profoundly changed biomedical research, as it greatly reduces the time and expense of developing animal models with specific genomic changes. Scientists now routinely use the CRISPR/Cas system for this purpose in mice. And for human diseases with a known mutation, such as cystic fibrosis, it’s theoretically possible to insert DNA that corrects the mutation. There are clinical applications in human trials now, including for engineering T cells outside of the body for CAR-T cancer therapy and for editing retinal cells for leber’s congenital amaurosis 10, an inherited form of blindness. LimitationsCRISPR/Cas is an extremely powerful tool, but it has important limitations. It is: difficult to deliver the CRISPR/Cas material to mature cells in large numbers, which remains a problem for many clinical applications. Viral vectors are the most common delivery method. not 100% efficient, so even the cells that take in CRISPR/Cas may not have genome editing activity. not 100% accurate, and “off-target” edits, while rare, may have severe consequences, particularly in clinical applications. Ethical issuesIn addition to editing somatic cells (the cells that make up most of the body), it’s possible to edit the genomes of gametes (eggs and sperm) and early embryos, called germline editing. Any such edits in humans would not only affect an individual but also his or her progeny. They could also theoretically be used to enhance desirable traits instead of curing disease. Scientists have therefore called for a moratorium on human germline editing until the serious ethical and societal implications are more fully understood.

# Private Jet 私人飞机

A private jet, business jet, or bizjet is a jet aircraft designed for transporting small groups of people. Business jets may be adapted for other roles, such as the evacuation of casualties or express parcel deliveries, and some are used by public bodies, government officials or the armed forces. Most production business jets use two jet engines as a compromise between the operating economy of fewer engines and the ability to safely continue flight after an engine failure. Exceptions include the early Lockheed Jetstar with four engines; the Dassault Falcon 50 and derivatives with three; and the Cirrus Vision SF50 with one, a configuration also used in several similar very light jet design concepts. Most business jets use podded engines mounted on the rear fuselage with a cruciform tail or T-tail to reduce interference drag and increase exhaust clearance. Practical limits on the ground clearance of these smaller aircraft have prompted designers to avoid the common jetliner configuration of a low wing with underslung podded engines. The sole business jet to use this layout, the early McDonnell 119, was rejected by the USAF due to foreign object damage concerns, leading to the failure of the program. The recent HondaJet uses wing-mounted engines but mitigates this problem with its unique over-the-wing engine pods. As with jetliners, swept wings are often used to increase cruise speed, but straight wings are also commonplace; notably, Cessna deliberately prioritized docile low-speed handling in choosing straight wings for many models in its popular Citation family, envisioning that owners transitioning from slower piston engined or turboprop aircraft would want to maintain the ability to use relatively short runways, and that lower approach speeds would ease single-pilot operations, particularly by relatively inexperienced owner-pilots. Rolls-Royce plc powers over 3,000 business jets, 42% of the fleet: all the Gulfstreams and Bombardier Globals, the Cessna Citation X and Embraer Legacy 600, early Hawkers, and many small jets with the Williams-Rolls FJ44.

# Spaceship 星际飞船

A spaceship is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, planetary exploration, and transportation of humans and cargo. All spaceship except single-stage-to-orbit vehicles cannot get into space on their own, and require a launch vehicle (carrier rocket). On a sub-orbital spaceflight, a space vehicle enters space and then returns to the surface, without having gained sufficient energy or velocity to make a full orbit of the Earth. For orbital spaceflights, spaceship enter closed orbits around the Earth or around other celestial bodies. spaceship used for human spaceflight carry people on board as crew or passengers from start or on orbit (space stations) only, whereas those used for robotic space missions operate either autonomously or telerobotically. Robotic spaceship used to support scientific research are space probes. Robotic spaceship that remain in orbit around a planetary body are artificial satellites. To date, only a handful of interstellar probes, such as Pioneer 10 and 11, Voyager 1 and 2, and New Horizons, are on trajectories that leave the Solar System. Orbital spaceship may be recoverable or not. Most are not. Recoverable spaceship may be subdivided by method of reentry to Earth into non-winged space capsules and winged spaceplanes. Recoverable spaceship may be reusable (can be launched again or several times, like the SpaceX Dragon and the Space Shuttle orbiters) or expendable (like the Soyuz). In recent years, we are seeing more space agencies tending towards reusable spaceship.

# Turbofan 涡轮风扇

Jet engines, which are also called gas turbines, work by sucking air into the front of the engine using a fan. From there, the engine compresses the air, mixes fuel with it, ignites the fuel/air mixture, and shoots it out the back of the engine, creating thrust. A turbofan engine, sometimes referred to as a fanjet or bypass engine, is a jet engine variant which produces thrust using a combination of jet core efflux and bypass air which has been accelerated by a ducted fan that is driven by the jet core. The FanThe first part of the turbofan is the fan. It’s also the part that you can see when you’re looking at the front of a jet. The fan, which almost always is made of titanium blades, sucks in tremendous quantities of air into the engine. The air moves through two parts of the engine. Some of the air is directed into the engine’s core, where the combustion will occur. The rest of the air, called “bypass air”, is moved around the outside of the engine core through a duct. This bypass air creates additional thrust, cools the engine, and makes the engine quieter by blanketing the exhaust air that’s exiting the engine. In today’s modern turbofans, bypass air produces the majority of an engine’s thrust. The CompressorThe compressor is located in the first part of the engine core. And it, as you probably have guessed, compresses the air. The compressor, which is called an “axial flow compressor”, uses a series of airfoil-shaped spinning blades to speed up and compress the air. It’s called axial flow, because the air passes through the engine in a direction parallel to the shaft of the engine (as opposed to centrifugal flow). As the air moves through the compressor, each set of blades is slightly smaller, adding more energy and compression to the air. In between each set of compressor blades are non-moving airfoil-shaped blades called “stators”. These stators (which are also called vanes), increase the pressure of the air by converting the rotational energy into static pressure. The stators also prepare the air for entering the next set of rotating blades. In other words, they “straighten” the flow of air. When combined, a pair of rotating and stationary blades is called a stage.