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Science Feature Articles</p>

Protecting Computer Systems and Communication Networks

English

One way of hiding information

 

Upgrading the confidentiality and authenticity of data communications and of computer-stored information is a major goal of leading cryptography experts at the Weizmann Institute's Faculty of Mathematical Sciences.

By studying and improving encryption techniques, they are developing new tools to ensure that computer files cannot be altered without detection and unauthorized users do not enter the system. By designing unforgeable digital identification systems, they are enabling verification of the authenticity of computer-to-computer communications and of network users. Institute computer scientists also investigate the theory of cryptographic transformations and random number generation, expanding basic knowledge in the field.

Before coming to the Institute in 1982, Prof. Adi Shamir was one of the developers of the extremely sophisticated RSA public key system. This benchmark cryptographic approach is currently used in many commercial software products and in secure telephone and network systems. In Rehovot, he and Dr. Amos Fiat designed a method that provides identification, authentication and signature facilities for digital communications, enhancing computer security. The procedure was patented by the Institute's Yeda Research and Development Co. and is presently used in various applications, including the programming of "smart cards" to ensure that only authorized subscribers can access satellite pay-TV.

"Zero-knowledge interactive proofs," a theoretical concept that underlies the Fiat-Shamir approach, was designed by Prof. Shafi Goldwasser when she was at MIT, working with her colleagues there and at the University of Toronto. This technique enables, among other things the transmission of an identification password in a way that provides no information about that password to an unauthorized eavesdropper. The wide applicability of zero-knowledge proofs was shown by Goldwasser's colleague Prof. Oded Goldreich, then also at MIT, who studied this with MIT and Berkeley scientists.

Goldwasser and Goldreich, both now at the Weizmann Institute, are improving the encryption of computer files, so that encrypting small changes in a large file does not require rescrambling the complete file. This advance may speed the use of scrambling to foil the spread of computer viruses or for preparing multiple authenticated documents. Goldreich is also developing ways to disseminate database information through multiple computers under different auspices, so that the database owner cannot record the information being requested.

The security risks associated with data transmission over public communication lines are also being addressed by Dr. Moni Naor. Such communication interactions include bank and computer-purchase transactions, as well as the transmission of medical records, proprietary data, and telecommunications. Naor is designing improved cryptographic schemes for dealing with these issues.

He also investigates "secret-sharing," techniques in which multiple keys held by different people are required to read or write confidential information. This idea is similar to the use of multiple signatures on checks. Naor and Shamir have recently implemented one of their concepts by designing a secret-sharing scheme for encrypting visual information.
Math & Computer Science
English
  • Adi Shamir
  • Applied Mathematics and Computer Science
  • Cryptography
  • Moni Naor
  • Oded Goldreich
  • Shafi Goldwasser

Mysterious Account of Agriculture in Masada Clarified by Institute Study

English

Dr. Dan Yakir. Ancient cellulose preserves record

A puzzling reference to "agriculture in the fortress of Masada" by Josephus Flavius, a noted Jewish historian and general of the first century A.D., may now be better understood thanks to a Weizmann Institute study recently described in Geochimica et Cosmochimica Acta. Based on chemical and isotopic analyses of wood preserved in the Roman rampart used in the storming of Masada, the study indicates that the climate in that extremely arid region was cooler and more humid two thousand years ago. Thus it may have been more feasible to engage in agriculture then than it is today.

The research was carried out by Dr. Dan Yakir and Prof. Joel Gat of the Institute's Department of Environmental Sciences and Energy Research, in Cooperation with Prof. Arie Issar of the Ben-Gurion University of the Negev.

Masada was the last Jewish fortress to hold out against the Romans after Jerusalem was conquered in 70 A.D. Josephus reports that Herod the Great (king of Judea from 37 to 4 B.C.), who had fortified the site, reserved the top of the hill for agriculture "for the preservation of those committed to the fortress." This reference has puzzled investigators of that period, since today's extremely arid climate in that region -- the eastern margin of the Judean Desert -- cannot support agriculture.

The Romans had stormed the fortress by advancing their siege machines over a rampart made largely of tamarisk wood covered by soil. This wood must have been of local origin since tamarisk trees are characteristic of the Masada region, while pine -- the most likely source of timber in higher elevations or the coastal plain -- was completely absent from the rampart. The researchers dug out samples of wood along this structure and compared the isotopic composition of its cellulose to that of cellulose from tamarisk trees growing in the region today.

The samples of ancient cellulose were found to be depleted in two stable isotopes -- carbon 13 (13C) and oxygen 18 (18O) -- as compared to the modern wood. Since higher 13C values result from stress factors such as drought or salinity, and higher 18O concentrations are associated with low humidity, the findings indicate that the climate was more amenable to agriculture two thousand years ago than it is now.

Dr. Yakir holds the Rowland Schaefer Career Development Chair. The research was supported by the German-Israel Fund.
Environment
English
  • Climate record
  • Dan Yakir
  • Environmental Sciences and Energy Research

Operation of Major Breast Cancer Drug Explained

English

Prof. Degani and Furman-Haran imaged tumor with MRI

One of the most puzzling aspects of the widely used breast cancer drug tamoxifen -- which shrinks estrogen-sensitive tumors yet is unable to kill cells from these tumors in tissue culture -- has been clarified by Weizmann Institute scientists working with doctors at the Sheba Medical Center near Tel Aviv.


The investigators found that tamoxifen destroys tumors by preventing them from maintaining their blood-capillary network. Without an adequately functioning life-support network, cancer cells die and the tumor regresses in size.

Participating in this study were group leader Prof. Hadassa Degani and graduate student Edna Furman-Haran of the Weizmann Institute's Department of Chemical Physics, Dr. Ada Horowitz and Iris Goldberg of the Department of Pathology of the Sheba Medical Center, and Dr. Antonio F. Maretzek, a visiting scientist from the University of Bremen.

Interest in tamoxifen stems from its wide use to prevent the recurrence of breast cancer in women who have undergone surgery to remove an estrogen-sensitive tumor. It is also being tested in patients in the United States and United Kingdom as an anticancer prophylactic in high-risk women.

Because only about half of breast tumors are estrogen dependent and potentially responsive to tamoxifen, the new Weizmann-Sheba study suggests seeking other drugs that destabilize the tumor capillary support system, and perhaps using them to control estrogen-independent breast tumors. Such new approaches could also complement tamoxifen therapy itself, as long-term treatment with the drug often leads to the appearance of estrogen-independent growths.

Using advanced magnetic resonance imaging (MRI) at high spatial resolution coupled with immunohistochemical techniques, Weizmann Institute and Sheba Medical Center researchers have studied how tamoxifen affects the growth of human breast carcinomas implanted in laboratory mice. They found that shortly after initiation of tamoxifen treatment, the tumors stopped growing and after two weeks, they showed an average 26% reduction in size and significant increase in the extent of necrosis. Specific histological staining of the endothelial cells comprising the microcapillaries showed a two-fold decrease in their density, indicating a reduced capacity of this tissue to deliver oxygen and vital nutrients.

This study was partially supported by the U.S.-Israel Binational Science Foundation and by the Israel Academy of Sciences and Humanities.
Life Sciences
English
  • Anticancer therapies
  • Breast cancer
  • Hadassa Degani
  • MRI

From Plato to Grinvald

English

Prof. Amiram Grinvald. Revealing the primary visual cortex

An article reviewing the development of man's understanding of vision, which recently appeared in the Journal of NIH Research, begins with Plato's theory of "visual fire" and ends with elucidation of functional organization in the visual cortex of the brain by Prof. Amiram Grinvald of the Institute's Department of Neurobiology.


According to the article, the first detailed theory of vision was propounded by early Greek philosophers such as Plato, who held that a ray of visual fire emanated from each eye and mixed with light to produce an invisible structure between the eye and an observed object. Galen, a second-century Roman physician, suggested that the brain is essential for consciousness and perception. In 1490, da Vinci reiterated Galen's concept that the eyes communicate directly with the brain. This long line of research, pursued by many scientists, was followed by the seminal work of Cajal and that of Hubel and Wiesel, who won Nobel Prizes for their contribution to brain research. And the most recent advances, according to the Journal, have been made by Prof. Gary Blasdel of the Harvard Medical School and the Weizmann's Prof. Grinvald.


"Independently," the Journal reports, "since 1986 they have used cameras to measure changes in the activity of neurons in exposed surfaces of the visual cortex as animals view lines of different orientations. They mapped the location of many different orientation columns on the surface of the primary visual cortex in a single test animal, at a higher resolution than is possible with standard methods of labeling."


The optical imaging technique that they used, which allows the direct visualization of electrical activity in the living brain, was developed by Grinvald at the Weizmann Institute in 1984. In enables scientists to visualize the intricate functional architecture of the brain, that is, the layout across the cortical surface of brain cells involved in distinct processing tasks. Optical imaging of functional borders is also being applied by neurosurgeons to minimize damage during tumor removal. The technique grew out of the 1968 pioneering work of Tasaki and Cohen showing that electrical activity of single nerve cells can be monitored by light.

Referring specifically to Grinvald's work, the Journal states: "He showed that the orientation columns are arranged in radially symmetric, fan-like structures he called 'pinwheels'. In this arrangement, a set of orientation columns intersects at the center of the pinwheel." This information sheds new light on the functional organization of the nerve cells responsible for the perception of object shapes. This work was done together with Prof. Tobias Bonhoeffer at Rockefeller University.

Thanks largely to these investigations, the NIH Journal concludes, "researchers currently understand the primary visual cortex better than any other part of the brain."
Prof. Grinvald, who holds the Helen and Norman Asher Chair in Brain Research, is the director of the Grodetsky Center for the Research of Higher Brain Functions.
 

Life Sciences
English
  • Amiram Grinvald
  • Brain research
  • Neurobiology
  • Optical imaging
  • Vision

Institute Mathematicians Define Economic Paradox

English

In seeming defiance of common sense, the demand for certain goods may actually soar when they increase in price. While this paradox, referred to as the Giffen effect, has been know for about a century, Weizmann Institute scientists have now developed a mathematical model that defines the real-life conditions under which it may appear.

The Giffen effect may occur when the price of an item that is vital for poor people goes up. For example, if the price of bread increases, the poor will no longer be able to afford related foodstuffs that are even more expensive, such as bagels. As a result, their entire budget for flour products will be spent on bread, driving the demand for this foodstuff upwards. This scenario was first proposed at the end of the last century by the English economist Sir Robert Giffen to explain why the demand for potatoes sharply increased following a price hike during the Irish potato famine of the 1840s.

Although the Giffen effect is highly uncommon because most people are not sufficiently poor to cause its occurrence, Prof. Yakar Kannai of the Institute's Department of Theoretical Mathematics and graduate student Shmuel Baruch have discovered this paradox in the modern Japanese economy. By conducting a statistical analysis of data on household expenditures in that country, they showed that the demand for the cheap alcoholic beverage shochu, drunk largely by poorer Japanese, increased when its price rose. This occurred because the poorer people stopped buying more refined and expensive brands -- namely, first- and second-grade sake -- spending all their drinking money on shochu instead.

Kannai and Baruch have also developed a mathematical model that makes it possible to determine whether the Griffen effect is possible in a given economy. The model consists of graphs and equations describing various conditions prevailing in that economy, particularly the interplay between the intensity of demand and the distribution of income.

According to Kannai, this model is valid only when the people behave rationally and know the quality of the goods. It does not take into account the "snob appeal" of certain overpriced items or the tendency of some people to opt for more expensive goods on the assumption that these are better than equivalent cheap goods.

Prof. Kannai is the incumbent of the Erica and Ludwig Jesselson Chair of Theoretical Mathematics.
Math & Computer Science
English
  • Mathematical model
  • Mathematics
  • Yakar Kannai

Improved Bone Marrow Transplants in Leukemia Patients

English

Researchers from the Weizmann Institute and Perugia University in Italy have developed a method that may significantly improve the chances for people with leukemia to receive potentially life-saving bone marrow transplants. Whereas today many leukemia patients fail to find properly matched marrow donors, the new approach -- whose effectiveness still needs to be confirmed in further studies -- may allow them to receive transplants from unmatched individuals, thus making marrow transplantation available to all those in need of the treatment.

The method was developed over the past eight years by Prof. Yair Reisner of the Institute's Department of Membrane Research and Biophysics and Prof. Massimo F. Martelli of the University of Perugia's Policlinico Monteluce in Perugia, Italy.

When the first 17 patients were treated in Italy with their technique, the donor marrow -- drawn from family members who were not entirely compatible with the recipients -- successfully implanted itself in 16 of the cases. Although all the patients had been in terminal stages of leukemia, six were free of the disease when study results were summed up.

Bone marrow transplantation (BMT), a last-resort treatment for leukemia and other disorders, consists of wiping out the patients' immune system and the diseased bone marrow, and infusing them with healthy marrow. Transplanting marrow from unmatched donors has been problematic because, despite the pre-treatment, the patients' residual immune cells may recognize the incompatible transplant as "foreign" and reject it.

The new approach eliminates the requirement for a very close match between donor and recipient by using up to ten times the normal amounts of transplanted marrow. Such "megadoses" appear to be effective because they give transplanted cells an edge in their competition with residual recipient cells, thereby minimizing the risk of rejection.

In addition, the collected marrow is purified using a technique developed by Reisner some ten years ago to enable "bubble" children with severe combined immunodeficiency diseases to undergo BMT. This multi-stage process -- which was also used in treating several victims of the nuclear accident at Chernobyl -- prevents a severe complication known as graft-versus-host disease.

Although the "megadose" method has thus far been tried only in people with leukemia, in the future it may be modified to treat noncancerous blood disorders, such as sickle-cell anemia, and to facilitate organ transplantation.
Life Sciences
English
  • Bone marrow
  • Leukemia
  • Membrane Research and Biophysics
  • Yair Reisner

Haim Harari Predicted Existence of Top Quark In 1975

English

Prof. Haim Harari. Presenting the full picture

When physicists at the Fermi National Laboratory in the U.S. observed traces of the top quark -- the remaining undetected member of this most important family of fundamental particles -- this sent waves of excitement throughout the scientific community. News of this discovery, widely covered in the media climaxed an over three-decade-long study of quarks -- the building blocks of matter governed by the strong nuclear force, namely, most of the visible material universe.

Unknown to many outside the field is the fact that one of the first physicists to suggest the existence of top quark and the one who gave it its name is Weizmann Institute President Prof. Haim Harari. In a 1975 paper in Physics Letters, Prof. Harari postulated that apart from the three species of quarks that had already been observed and a fourth one which was just discovered there was a theoretical "need" for two additional heavy quarks with charges of 2/3 and -1/3. He named the two new proposed quarks "top" and "bottom," names that remain in use today.

The original model, presented then by Harari, needed major modifications, but a few months later in his rapporteur lecture at the year's International Conference on particle physics, Harari presented for the first time the full correct picture of the world of quarks and leptons, as we know it today, consisting of six species of quarks and six species of leptons. That picture has become the standard understanding. It was followed by the discovery of the bottom quark in 1977.

Commenting on the new Fermilab data, Harari says that while seeing traces of the top quark was of major importance, physicists were convinced of its existence for the last 19 years. But because the top quark has the largest mass of all quarks, experimental evidence about it could only be gathered with accelerators operating at the cutting edge of high-energy technology, a situation that delayed its detection.

Elementary particle physics has matured considerably since 1975, and it is now known that the experiments around which Harari built his early theory were not correctly interpreted. Nevertheless, subsequently gathered data have provided a firm basis for the presently accepted Standard Model of the material universe, which assumes -- as Harari did -- a six-member family of quarks.

This work, says Harari, is still far from complete. For one, the measurement of the top quark at Fermilab still needs further conformational studies. In addition, the theoretical relationship between the quarks and the second central family of particles, the leptons, still has to be ironed out, several different approaches having already been formulated. Whatever future developments will be, the excitement surrounding particle physics shows no signs of dying down.

Prof. Harari occupies the Annenberg Chair of High Energy Physics.
 

Need for additional quarks

 
Space & Physics
English
  • Haim Harari
  • Particle Physics
  • Theoretical physics›Theoretical particle physics
Yes

Sun-Protection Mechanism of Plants Unraveled

English

Prof. Zamir. Secrets of sun-resistance

 
Agricultural crops resistant to strong sunlight may one day be cultivated in the hottest and most drought-ridden parts of the world thanks to recent finding of Weizmann Institute researchers.

The scientists have unraveled the protective mechanism allowing a particularly sturdy salt-water alga, Dunaliella bardawil, to thrive in scorching sunlight. In the future, it may be possible to manipulate a similar mechanism existing in higher plants, including crop, in order to enhance their resistance to the sun, according to Prof. Ada Zamir of the Institute's Department of Biochemistry. She deciphered the mechanism together with department members Haim Levy, Tamar Tal, Dr. Aviv Shaish, Dr. Irena Gokhman and Dr. Amnon Lers.

Dunaliella bardawil is known for its legendary resistance to the salt and sun, which allows it to thrive in the brackish marshes of the Sinai desert and even in the Dead Sea. It was first isolated from the Bardawil marsh in Sinai and studied by the late Institute Professor Mordhay Avron, together with his then student, Prof. Ami Ben-Amotz.

The dunaliella alga fascinates scientists because it is both a remarkable survivor and functionally very similar to higher plants. These two properties make it an excellent model for studying survival strategies that may be relevant for growing useful crops under harsh conditions, according to Prof. Zamir.

Excessive sunlight causes most plants to produce toxic oxygen molecules that damage and eventually destroy the plant's photosynthetic machinery. Zamir and her associates have discovered a protein, now known as Cbr, that is formed in dunaliella whenever this machinery is threatened. Using genetic engineering, the researchers have cloned the gene coding for this protein.

They further observed a close link between Cbr and a carotenoid pigment called zeaxanthin, also formed under the stressful conditions of intense light. The scientists have concluded that the protein binds with the pigment to form a light-protective "antenna" or "lightening rod," which diverts the excessive, harmful light from the sensitive components of the photosynthetic machinery. While producing Cbr and zeaxanthin, the alga also forms large quantities of beta-carotene, an orange pigment that serves as the plant's natural sunscreen.

Prof. Zamir holds the Carl and Dorothy Bennett Chair of Biochemistry.

The research was supported by grants from the Minerva and the German-Israel Foundations.
 
Environment
English
  • Ada Zamir
  • Alga
  • Dead Sea
  • Genetic engineering
  • Plant Sciences

Mysterious Radiation Bursts Explained

English

 

Compton Gamma Ray Observatory. Throwing light on gamma radiation
 
 
Mysterious bursts of gamma rays detected in outer space are caused by the birth of neutron stars that spin at a dizzying 1,000 revolutions per second and have extremely strong magnetic fields, according to Weizmann Institute astrophysicist Vladimir Usov.

Prof. Usov, a member of the Institute Department of Condensed Matter Physics, developed this theory after analyzing vast amounts of information obtained by NASA's orbiting Compton Gamma Ray Observatory. He has recently described his views in the British journals Nature and Monthly Notices of the Royal Astronomical Society.

Most scientists attribute the extraordinary gamma ray bursts to the merger, or death, of neutron stars that results in the creation of black holes. Usov argues that, on the contrary, the bursts take place when neutron stars are born under certain conditions.

He proposes the following scenario: a white dwarf (a hot, dense star giving off white light) that possesses a powerful surface magnetic field draws matter from another, nearby star. When a certain critical mass is reached, the dwarf collapses and forms a fast-rotating neutron star with a magnetic field more than a few million billion times greater than that of the earth.

The spinning of this field produces a strong electric field surrounding the neutron star, which generates a gas known as electron-positron plasma. This plasma flows away from the star at nearly the speed of light, creating a gust of extremely dense, magnetized wind that is detected by satellites as a powerful gamma-ray flash lasting from a fraction of a second to a few minutes.

First observed some 25 years ago, gamma ray bursts are currently detected at the rate of about one per day in galaxies throughout the universe.

According to Prof. Usov, understanding processes involved in the birth of neutron stars not only throws light on the origins of gamma radiation in the universe but may also provide scientists with a unique opportunity to observe and study matter subjected to extreme conditions, such as enormous magnetic fields. "Learning about faraway galaxies on the basis of observations may eventually allow us to turn outer space into a huge lab," Usov says.

Prof. Usov, formerly with the Space Research Institute of the USSR Academy of Sciences in Moscow, joined the Weizmann staff in 1990.
 

Prof. Vladimir Usov. Birth of a star

Space & Physics
English
  • Astrophysics
  • Condensed Matter Physics
  • Gamma ray
  • Vladimir Usov

Compound to be Tested on AIDS Patients

English

Profs. Yehuda Mazur and Prof. David Lavie. Neutralizing viruses

 

Hypericin, a compound whose antiviral properties were first documented at the Institute, is now being tested on AIDS-afflicted patients at three American research hospitals.


In the early 1980's Prof. David Lavie of the Department of Organic Chemistry began to investigate whether Hypericum triquetrifolium, a plant that grows wild in Israel, possesses the same medicinal qualities as Hypericum perforatum, a plant popularly known as St. John's wort, which has long been used as an antidepressant. Lavie isolated one of the plant's active ingredients, hypericin, and found that it has antiviral activity.

Prof. Lavie's son, Dr. Gad Lavie, then working at New York University Medical Center, discovered that hypericin suppresses the action of two animal retroviruses. Test-tube experiments carried out in a joint Weizmann Institute -- New York University Medical Center study subsequently showed that hypericin is active against yet another retrovirus, the human AIDS virus HIV. A Weizmann Institute team headed by the senior Lavie and Prof. Yehuda Mazur, also of the Department of Organic Chemistry, proceeded to synthesize the active substance hypericin and to elucidate its chemical properties.

Laboratory tests of this material by the New York Blood Center recently achieved complete inactivation of over 100,000 HIV particles per milliliter of human blood -- a concentration around 100 times greater than that typically found in infected blood plasma. Investigations at this center have also begun on the use of hypericin to neutralize a wide range of other viruses and retroviruses present in stored human transfusion blood, and into ways of removing the hypericin once the blood has been made safe.

Clinical trials sponsored by the U.S. National Institutes of Health (NIH) recently examined the inherent safety of hypericin when given intravenously to HIV-infected patients. A 24-patient NIH-sponsored PhaseI/II trial of an oral form of the drug is now getting under way at NYU Medical Center/Bellevue Hospital, Beth Israel Hospital in Boston and Johns Hopkins University Hospital in Baltimore.

Hypericin for these studies is manufactured by VIMRx Pharmaceuticals of Stamford, Connecticut, under a license granted by Yeda Research & Development Co., which is responsible for the commercial applications of Weizmann research.

Prof. Mazur holds the Rebecca and Israel Sieff Chair of Organic Chemistry, and Prof. Lavie, the Israel Matz Chair of Organic Chemistry.
 
Hypericum triquetrifolium plant grows wild in Israel
 

 

 
 
Life Sciences
English
  • David Lavie
  • HIV
  • Organic Chemistry
  • Virus
  • Yeda
  • Yehuda Mazur

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