Author: SD

Dielectica traverses through the literature on this topic – and summarizes as they appear.

Correspondence prepared by: Sayan Bayan¹ and Suman Chakraborty², ¹S. N. Bose National Centre for Basic Sciences, Kolkata, India, email: sayan.bayan@gmail.com, ²Physical Research Laboratory, Gujrat, India, email: suman.chakrabarty37@gmail.com (16:10:2020 and 14:00)

Key Words: Black holes, Event horizon, General Theory of Relativity, Singularity

India: The Nobel Prize in Physics for the year 2020has been awarded in one half to Roger Penrose“for the discovery that black hole formation is a robust prediction of the general theory of relativity” and the other half jointly to Reinhard Genzel and Andrea Ghez “for the discovery of a supermassive compact object at the centre of our galaxy”. Henceforth, the three scientists shared this prize for their outstanding discoveries about the ‘black hole’ which is considered as one of the most mysterious themes in Physics. To give a thought on their discovery, one needs to understand what are black holes and why are they so mysterious?

A black hole can be defined as a region in space where gravity is so strong that even light cannot escape through it. The black hole is enclosed by a boundary called ‘event horizon’ which defines the region where the velocity required to escape exceeds the speed of light [1]. Such strong gravity originates from the fact that matter gets squeezed into a very tiny space. Such a situation can be realized during the death of a star having mass more than three times the mass of the Sun. Since light cannot get out of black holes, it is conventionally invisible in naked eyes. However, a black hole can be realized by the virtue of its gravitational pull on other stars around it. The strong gravitational force of a black hole will pull matter from other stars. During this process, the compression and heat generation (in millions of degrees) will lead to the production of X-rays that radiate in space. Thus the outward region of the black hole can be realized by the emission of X-rays. In many occasions, the spreading of radio waves has also been witnessed [2].

Now back to the past, theoretically, the existence of black holes has been traced from Einstein’s general theory of relativity, although Einstein himself denied the concept of black holes. According to this theory, the force of gravity arises from the warping of spacetime (fusion of three dimensional space and one dimensional time) around a body. The core of this theory is some nonlinear equations known as Einstein field equations. Soon after the appearance of this theory, Karl Schwarzschild found the non-trivial solution of the Einstein field equations which led to the concept of gravitational collapse and the condition of singularity [3]. A singularity is a location where the gravitational field becomes infinite. However, the concept of singularity was debated a lot as many scientists attempted to prove that singularities don’t appear in generic solutions. In 1955, A. K. Raychadhuri’s work remarkably transformed the field of general theory of relativity as the equations laid by him formed the basis of all singularity theorems [3]. The defining moment came with the singularity theorem in 1965 where Penrose sparked the idea of incompleteness to describe singular spacetime and for the first time he introduced the concept of a closed trapped surface. The concept of a closed trapped surface reveals the inner region of an event horizon and can be assumed as the surface from which light is not moving away. Thus Penrose established that singularities appear generically and concluded with his Nobel winning discovery. Penrose’s singularity theorem was ample and straightaway and led to the development of modern singularity theorems [3].      

Penrose established the existence of black holes theoretically, while teams led by Ghez and Genzel’s demonstrated experimental evidence of such celestial giants at the heart of our Galaxy. Since a long time physicists suspected that most galaxies include a supermassive black hole at the centre. The bright Sagittarius A* (Sgr A*) – a radio source situated at the centre of Milky Way, was suspected as a black hole. In the 1980s, Genzel and Charles Townes (another Nobel laureate) exploited InfraRed (IR) spectroscopy to track gas clouds orbiting at the centre of the Milky Way. Although they could infer the presence of a massive, compact source of gravitation, the evidence was not ultimate.

The prime challenge was to detect the emission from the stars amidst the gas and dust obstacles. However in 1990, teams led by Ghez and Genzel came out to address this issue with the world’s biggest telescopes which work in the near-IR region suitable for sensing the light that can escape the dusty region of the galactic centre.  Ghez and her team used the Keck Observatory, Hawaii, while Genzel and his co-workers used the Very Large Telescope on Cerro Paranal, Chile. With a series of developments in imaging techniques, they could improve the resolution and sensitivity to the faint light from the celestial world.

The two teams tracked and plotted the tracks of several stars near the centre of the galaxy for a decade, particularly the star called S0-2 by Ghez’s group or S2 by Genzel’s team.  This led to the understanding that the motion and pattern of the stars are influenced by the presence of an invisible source of four million solar masses and which is certainly a supermassive black hole [4]. This was not only the strongest evidence of the presence of the giant black hole at the galaxy’s core, but also stimulates research on the immense gravitational effects on its stellar neighbours.

Sources:
[1] https://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-is-a-black-hole-k4.html
[2] https://science.nasa.gov/astrophysics/focus-areas/black-holes
[3] J. M. M. Senovilla, D. Garfinkle, Class. Quantum Grav., 32, 124008 (2015).
https://iopscience.iop.org/article/10.1088/0264-9381/32/12/124008
[4] www.timesonline.co.uk/tol/news/uk/science/article5316001.ece

Dielectica traverses through the literature on this topic – and summarizes as they appear.

Correspondence prepared by: Dr. Md Palashuddin Sk, Assistant Professor of Aligarh Muslim University, Uttar Pradesh, India, email: palashuddin.ch@amu.ac.in (12:10:2020, 17:30)

Key Words: Haemoglobin, Carbogenic Dots, luminescence, nanocrystals

Aligarh: Haemoglobin (Hb) is an essential iron-containing protein, which exists in the red blood corpuscles. Hb consists of four iron-porphyrin units (heme) together with the globular protein moiety. Atomic iron encaged into the heme moiety plays a crucial role in transporting molecular oxygen (O₂) from the respiratory organs to the different parts of our body through blood and carrying the major portion of carbon dioxide from these parts to the lungs at the same time. The Hb level in blood to the well-functioning of the organism in the human body is 13.0-18.0 g/dL and 12.0- 16.0 g/dL for male and female, respectively [1]. On the contrary, Hb amount below this level solely causes several blood disorder diseases (even fatality) such as thalassemia, anaemia, and leukaemia. Approximately, two billion people (mainly women and children), worldwide suffer from particular anaemia due to the lower level of Hb in blood. The lower level of Hb thus becomes a major issue and hence is of substantial significance for clinical diagnosis purposes. In this regard, the sensitive detection and determination of Hb in clinical diagnostics is essential to assess the extent of blood disorder diseases and to evaluate various intervention programs aimed at control of the same.

There are quite a few analytical methods like electrochemical, colorimetric, and various spectroscopic techniques are generally employed for the detection of Hb in the blood. Unfortunately, most of these techniques require harsh, expensive chemicals, tedious and complicated probe preparation and of low sensitivity detection ability as well.  In this scenario, the luminescent carbogenic dots (Cdots) are paid great attention due to their higher water solubility, biocompatibility, high quantum yield, and excellent optical (stability towards the chemical/physical environment changes such as pH, ionic strength, etc.) and well enough chemical stability.

Following this trend, our Research Group at Aligarh Muslim University, India, has recently developed a Hb sensor from the reaction by-product, which is accidentally isolated during the synthesis of tin oxide (SnO₂) nanocrystals [1]. The purified by-product is confirmed as luminescent carbogenic dots which is again produced due to the polymerization and consequent carbonization of the excess of 4,7,10-trioxa-1,13-tridecanediamine (TTDDA). Yet, TTDDA is a hazardous reagent, it is used as a stabilizing agent in metal nanocrystals synthesis [1]. The advantage of such synthesis lies in the fact that the obtained product SnO₂ nanocrystals and the reaction side product are environmentally friendly and are produced through the sustainable way. Our Research Group has actually employed the principle of luminescence turn-off property of Cdots with the interaction of Hb to develop a diagnostic method for qualitative and quantitative detection of Hb in the blood. The observed luminescence property of the Cdots remains highly selective towards the detection of a trace amount of Hb. Efficient ground state complexation between Cdots and Hb is solely responsible for the unprecedented selectivity of Cdots towards Hb detection. Keeping in mind the issues of accuracy in the visual detection, economic factors and the portability, we have further developed a fluorescent test strip-based sensing method. The rapid sensing experiment by using the fluorescent test strip has also been studied with the voluntary collection of blood samples, and various interfering chemical substances, proteins, amino acids, metal ions, anions, etc at pH ~7.4 in order to realize the selectivity as well. Upon addition of Hb, the emission intensity of Cdots is drastically reduced; while, in the case of other analytes addition, hardly any reasonable change in the intensity observed, validating the accuracy of the test strip. Test strip-based luminescence turn-off property of Cdots in the presence of Hb further defines their applicability in fabricating portable and inexpensive sensing devices. Even the trace amount of blood present in the human urine is also possible to be detected by this paper-based method, the author stated. The present paper strips based detection technique has advantages over conventional methods (absorption-based spectroscopic methods) because of the portability, cost-effectiveness, time-saving, high sensitivity, ease to measuring Hb, requiring minimum instrumentation and so forth. The user-friendly nature of this technique is quite desirable and beneficial mainly in the remote areas or primary health care centres to monitor the Hb level of patients.

Sources:
[1] F. Arshad et. al., New J. Chem., 44, 6213 (2020)
https://pubs.rsc.org/en/content/articlelanding/2020/nj/d0nj00401d#!divAbstract

By Dr. Amaresh Kumar Sahoo, Assistant Professor,Department of Applied Sciences, IIIT Allahabad, India; Email:asahoo@iiita.ac.in

The 2020 Nobel Prize in Physiology or Medicine is awarded to Prof.Harvey J. Alter, Prof.Michael Houghton and Prof.Charles M. Rice “for the discovery of Hepatitis C virus“. This is a blood-borne disease that has been the reason for more than a million deaths and caused a major health problem around the globe. The viral infection is the leading cause of different types of Hepatitis, with some of its forms that remained dormant for years until developed life-threatening symptoms. Much appreciation to Prof. Harvey J. Alter, Prof.Michael Houghton and Prof.Charles M. Rice for their groundbreaking discoveries that led to the identification of causative agent of this blood-borne disease, a novel virus, Hepatitis C Virus. The committee members of the Nobel Assembly at Karolinsky Institute in Stockholm, Sweden issued several statements regarding the revolutionary impact of this pioneering discovery in understanding the causes and cure for chronic Hepatitis. They added, “for the first time in the history, the disease can now be cured and it also raises hope of eradicating the disease caused by Hepatitis C virus from the world population”.

Infection sources of liver dysfunction and other health issues like fatigue and vomiting. This also causes jaundice characterized by yellow pigmentation of eyes and skin. Moreover, it may cause acute and chronic infections to lead to serious health complications like liver cancer or Cirrhosis. The cases of Hepatitis were seen upsurge rapidly since 1960 due to the increased number of surgeries and multiple blood transfusions. In World Health Organization (WHO) report around 1.34 million deaths mainly due to Hepatitis C virus infections were reported in 2015, which is approximately 63% increase in cases since 1990. Originally only Hepatitis Type A and Hepatitis Type B were known. The discovery of a vaccine for Hepatitis type B partially reduced the risk but chronic liver damage and liver cancer persisted. In the 1970s, Harvey Alter, a senior investigator for the National Institutes of Health in Maryland discovered a new type of Hepatitis Virus while studying the blood transfusion among the patients at the U.S. National Institutes of Health. Later, Michael Houghton, a British Scientist while working for a pharmaceutical firm Chiron then, dedicatedly put the strenuous effort in isolating the genetic sequence of the virus and given a name to this unknown virus as Hepatitis C Virus in 1989. Subsequently, Professor Charles M. Rice consistently worked at the Center for the Study of Hepatitis C as Scientific and Executive Director from 2001 to 2018 at Rockefeller University at New York and provided the final pieces of evidence stating that Hepatitis C Virus alone could cause Hepatitis. This is a RNA virus, which is having envelope glycoproteins such as E1 and E2 on the outside of the viral surface. The hepatitis C virus (HCV) causes hepatitis C, which is contagious in nature, and an infected person may transmit it to a non-infected person via blood contact. Therefore, the transfusions of unscreened blood and blood products or unsterilized medical setups have been found to be the major route of the transmission of HCV infections. It would be mentioned here that different genetic variations (genotypes) are present in the case of HCV strains. Thus, the prescription of the medicines is done based on the genotype of infection of HCV.  Use of combination therapy of recombinant interferon (IFNα) and the nucleoside analogue ribavirin was being recommended initially. However, several side effects and risks factors limit their widespread usages. In this line of interest, the development of drugs was proposed by specifically targeting the viral RNA-dependent RNA polymerase or other vital proteins.

The work of these three Nobel Laureates distinctively characterizes this form of Hepatitis from other clinical entity and found to be caused by an RNA virus of the Flavivirus family, termed as Hepatitis B virus. It is a milestone achievement that paved the way for the introduction of a new screening technique and an effective antiviral drug in medicine that could dramatically reduce the risk of Hepatitis C infection. 

Ref : https://www.nobelprize.org/prizes/medicine/2020/summary/#main-navigation-js

Dielectica traverses through the literature on this topic– and summarizes as they appear.

Correspondence prepared by: Suman Chakraborty, Physical Research Laboratory, Ahmadabad, Gujrat, India, email: suman.chakrabarty37@gmail.com (05:10:2020, 18:30 IST)

Key Words: Magnetosphere, Radiation belts, Space environment, Radiation Belt Storm Probes

Ahmedabad, India: Any planet that has a magnetic field is capable of deflecting charged particles travelling towards it and forms a protective cavity around itself called the magnetosphere. Besides shielding the planet from charged particles, the magnetosphere is also capable of trapping charged particles along magnetic field lines, forming a region called the radiation belts. The Earth’s radiation belts were discovered in 1958 by James Van Allen, a physicist at the University of Iowa using a simple cosmic ray experiment consisting of a Geiger counter and a tape recorder on the first US satellite, Explorer 1. During the flight, radiation levels seemed to increase and then suddenly drop to zero and then again to increase followed by a further sudden drop to zero. What the team soon realized was that regions appearing as zero were really off the scale! These high-radiation regions were mapped and identified as the radiation belts which are now often dubbed as the “Van Allen Radiation Belts” after the name of James Van Allen [1].

So, what are the radiation belts?
The Earth’s radiation belts are two giant donut-shaped regions of magnetically trapped, highly energetic charged particles with the Earth sitting at the center of the “donut hole”. It comprises of an inner belt and an outer belt with a “slot region” separating the two belts [1,2].

The figure shows the Van Allen Radiation Belts with the Earth at its center. We can clearly see a two-belt structure with a region of depleted charged particles in between the two belts. Although numerous studies have been conducted for the past several decades, the most prominent outcomes came since the launch of the Van Allen Probes in 2012. The Van Allen Probes (VAP; 2012 – 2019), initially known as the Radiation Belt Storm Probes (RBSP), were two identical spacecrafts that were deployed to study the Van Allen Radiation Belts. NASA conducted the VAP mission as part of the “Living with a Star” program. It was initially planned for 2 years, but eventually operated for 7 years. The probes showed that the radiation belts are even more complex than previously imagined and the shape of the belts depends on what particles are being studied. Such observations are more important today as our society now relies on more than 800 satellites operating in the radiation belts for communication and navigation. Dr. David Sibeck, VAP mission scientist at NASA’s Goddard Space Flight Center in Maryland, in a 2018 statement said, “Our current technology is ever more susceptible to these accelerated particles because even a single hit from a particle can upset our even smaller instruments and electronics. As technology advances, it’s actually becoming even more pressing to understand and predict our space environment“[1].

Part of interest to study the radiation belts came from its location. It is known that the radiation belts can expand and contract depending on solar activity. During intense solar activity, the belt can expand and even extend over the orbit of the International Space Station (ISS; Orbit height: 408 km). The ISS has been permanently inhabited since 2000, with typical astronauts staying there for six months at a time. In 2015 – 2016, NASA astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko remained there for almost a year. As astronauts stay in orbit for longer duration, their radiation exposure may also increase, leading to concerns about long-term habitation for astronauts in space. The knowledge of space environment is also necessary to design future spacecrafts in order to prevent them from short out due to an electrical overload that may lead to disruption of communication. All these aspects make the radiation belts a hot topic of research for the space science community. In an August 2016 NASA statement, Dr. Sibeck said, “We study radiation belts because they pose a hazard to spacecraft and astronauts. If you knew how bad the radiation could get, you would build a better spacecraft to accommodate that” [1].

Sources:
[1] https://www.space.com/33948-van-allen-radiation-belts.html
[2] https://www.nasa.gov/mission_pages/rbsp/mission/fun-facts.html