While our distant ancestors did not use a knife and fork the way we do, they had flint - a hard rock used to create tools for hunting, cooking and building. But making these tools, it turns out, was far from easy. Flint tends to crack and wither when exposed to atmospheric weathering. While know-how for producing flint existed already 2.5 million years ago, only with time did our ancestors learn how to obtain durable production materials: their secret was to dig - obtaining flint from mines rather than surface deposits - and their idea proved to be a pivotal technological advance, with important intellectual and cultural fringe benefits.

Dr. Elisabetta Boaretto of the Environmental Sciences and Energy Research Department recently traced this cultural transition.

Working with Prof. Steve Weiner, head of the Helen and Martin Kimmel Center for Archaeological Sciences, and with Prof. Micha Hass of the Particle Physics Department, Boaretto used a nuclear physics technique to determine whether flint samples from the prehistoric caves of Tabun (in the Carmel) and Qesem (near Rosh Ha’ayen) were produced from surface or underground deposits.

“When the flint (silicon dioxide) is exposed on Earth’s surface, it produces beryllium 10 through an interaction between cosmic rays and the oxygen in the silica mineral,” explains Boaretto. “If the same material is buried about two meters below the surface, this effect is reduced to a negligible level. Our assumption was that tool samples made of flint collected from surface deposits would have measurably higher Be¹⁰ levels than those derived from mined flint.”

Using the Institute’s Koffler pelletron accelerator to measure beryllium 10 concentrations, Boaretto and her colleagues found that flint samples collected from one layer of the Tabun Cave deposited about 350,000 years ago had beryllium 10 levels similar to mined material. In contrast, those found in the Qesem Cave, from about the same period, had a beryllium 10 distribution consistent with flint gathered from above ground or from shallow quarries. Were the people of Tabun pickier - i.e. more advanced - in choosing the raw material for their flint tools than their neighbors in Qesem? The data suggest so, but more research is needed.

Other scientists collaborating in this research are: Prof. Michael Paul and postdoctoral fellow Dr. Giovanni Verri of the Hebrew University and Prof. Avi Gopher and Dr. Ran Barkay of Tel Aviv University.

From Padua to Rehovot

Elisabetta Boaretto came to Israel from Padua, Italy, for her Ph.D. in physics at the Hebrew University with Prof. Michael Paul. As part of her experimental work, she used the Koffler pelletron accelerator at the WIS (which is where she met her Israeli-born husband, Dror Kella, also a physicist) to measure rare radioisotopes from ice cores in Greenland and Antarctica. The couple later pursued postdoctoral studies at Aarhus University in Denmark. They have two children, Eyal and Iris.

Prof. Weiner’s research is supported by the Helen and Martin Kimmel Center for Archaeological Sciences; the Women’s Health Research Center; the Philip M. Klutznick Fund; the Alfried Krupp von Bohlen und Halbach Foundation and Mr. George Schwartzman, Sarasota, FL. He is the incumbent of the Dr. Walter and Dr. Trude Borchardt Professorial Chair in Structural Biology.

Digital technology may well be the most significant advance of our time. But, as a team of scientists at the Weizmann Institute has shown, computers and DVD players have nothing on living cells, which have their own built-in digital systems.

Dr. Uri Alon, of the Molecular Cell Biology and Physics of Complex Systems Departments, along with team members Dr. Galit Lahav Shenhar, Nitzan Rosenfeld, Alex Sigal and Naama Geva-Zatorsky, discovered the phenomenon while investigating what is possibly the most researched protein ever - the tumor suppressor p53. Produced in the cell when DNA is damaged, p53 plays a role both in DNA repair and in a “self-destruct” command that switches on in the cell when damage is too great, preventing it from turning cancerous.

Probing the life cycle of this useful protein, the team saw, to their surprise, that p53 appears and disappears in regular, identical peaks, or pulses. This rhythmic pattern was completely at odds with previous findings suggesting that p53 is churned out in ever-increasing amounts as more damage is inflicted on the DNA. Each pulse recorded by the team involved the same amount of the protein and lasted for the same length of time (approximately five hours). When the amount of damage to DNA was increased, additional pulses ensued, but the size and duration of each remained stable. These pulses are like the tiny bits of information on a digital compact disk, which encodes sound using only two discrete possibilities: on or off. This is in contrast to analog-based technologies, which use the physical aspects of material to represent information, depicting it as changing continuously over time and space - similar to the grooves in a phonograph record, whose variations in depth generate ascending and descending tones.

“Digital technology has clear advantages over analog-based devices, in that it stands up well to a certain amount of noise and component imperfection, and is easier to manipulate. The cell may have evolved digital methods for similar reasons,” says Alon.

How did Alon and his team manage to observe this phenomenon, which literally thousands of others had missed? The answer lies in their non-conventional approach. Almost all previous studies of the dynamics of proteins like p53 have been done on material extracted from a large number of cells. Such studies give an average result over an entire cell population. In contrast, the Weizmann team decided to go after specific proteins in their natural setting, inside the walls of individual cells.

To accomplish this feat they applied a recent advance in genetic engineering, in which a segment of a jellyfish gene that encodes for bright fluorescent colors is inserted into the gene for the protein studied, thereby producing glowing protein molecules that can be easily distinguished under the microscope.

The p53 protein was colored with a cyan fluorescing marker, and MDM2 - another protein, responsible for dismantling p53 - was marked with yellow.

“The time-lapse sequence looked like a traffic light, with lights shining cyan, then yellow, then cyan. There was no mistaking that we were seeing something out of the ordinary,” says Alon.

Alon and his group plan to continue researching p53 and MDM2 in single cells, as they believe that the method may provide answers to some long-standing questions, such as how p53 mediates the switch from repair to suicide mode. Their findings are also important for others studying protein dynamics: “If we found one digital system, it’s likely there are others. We showed there are some phenomena that can be seen only by looking inside individual living cells,” says Alon.

Nights in the lab

Dr. Galit Lahav Shenhar, who created and led this project, was in charge of collecting the data using the fluorescence microscope. Because the cellular processes studied are relatively slow, the research required repeated 16-hour vigils, with cell photos taken every 15 minutes. “At that time, the system had to be refocused for each frame.

My lab partners were very supportive,” says Lahav. “Even my boyfriend (now husband), who is not a biologist, learned to work the microscope so I could get a few hours rest in the afternoon and come back to work until two or three in the morning. It was monotonous work, but the excitement of what we had discovered spurred me on. We might have thought our method was flawed, since the results were so unexpected, but Uri taught us to trust what we see, not what we expect to see.” The team now has a fully automated microscope, developed by Prof. Zvi Kam of the Molecular Cell Biology Department and computer scientist Yuvalal Liron, making the new generation of experiments much easier to perform.

Dr. Alon’s research is supported by the Charpak-Vered Visiting Fellowship, Canada; the Clore Center for Biological Physics; the Yad Abraham Research Center for Cancer Diagnostics and Therapy; the Estate of Ernst and Anni Deutsch, Lichtenstein; the Leon and Gina Fromer Philanthropic Fund; the Minerva Stiftung Gesellschaft fuer die Forschung m.b.H.; the James and Ilene Nathan Charitable Directed Fund; the Harry M. Ringel Memorial Foundation and Mr. and Mrs. Mordechai Segal, Israel .

May God bless and keep you always

May your wishes all come true

May you always do for others

And let others do for you.

May you build a ladder to the stars

And climb on every rung

May you stay forever young

Forever young, forever young

May you stay forever young.

-- Forever Young.  Music and lyrics: Bob Dylan

Will the universe - born, according to the widely accepted theory, some 15 billion years ago in the Big Bang - end with a whimper? Prof. Shaul Hanany, currently of the University of Minnesota and soon to join Weizmann’s Particle Physics Department, hopes to shed light on this question by measuring cosmic microwave background radiation, a relic from the Big Bang.

According to the Big Bang theory, the entire visible universe, including all its matter and energy, once occupied a tiny, extremely hot and dense region. At some stage, and for a yet unknown reason, this region began to expand - voila: the Big Bang. During this expansion, matter dispersed in all directions and resembled a thick primordial soup.

But how, ask cosmologists, did the current structure of the universe emerge from this primordial soup? Had the original soup been entirely uniform, clumps of matter such as the galaxies would not have formed; today’s universe would still be a continuous, uniform soup, with no galaxies, stars or, of course, humans probing its nature.

The existence of distinct clumps of matter has led cosmologists to hypothesize that different areas of the primordial soup were indeed distinguished from one another by minute variations in density, much like ripples or wrinkles. With time, and under the influence of gravity, these wrinkles intensified, causing the denser areas to give rise to the galaxies and stars known today, while the less dense areas gave rise to enormous empty spaces.

This hypothesis was confirmed in April 1992, when NASA’s satellite COBE succeeded in peeking back in time to when the universe was only 300,000 years old. COBE found tiny variations in the microwave radiation arriving from different locations in the universe - providing support for the notion of differences in the density of ancient matter. The song of these ripples is that of a forever young universe. “In the very young universe, radiation was tied to matter; the two were separated only when matter dispersed and cooled down,” explains Hanany. “However, because of their common past, the differences in radiation measured today still accurately portray density differences in matter and energy way back in time.”

Some of the most precise mappings of cosmic background radiation were obtained in two experiments co-led by Hanany. The results from one of them were subsequently selected as one of the ten most important scientific discoveries of the year 2000 by the editors of Science magazine. Both experiments used research balloons - one was launched in Texas and landed there; the other was launched in Sweden and landed in Siberia.

Analyzing the data from these experiments, Hanany and his colleagues inferred the total density of matter and energy in the universe with unprecedented accuracy - a finding that led to the conclusion that space is flat. Einstein’s equations allow for both flat and curved geometries for our space. Now we know which of those is realized in nature.

Drawing on additional astrophysical data the team also calculated the densities of different types of matter and energy, showing that the “regular” matter with which we are all familiar and from which we are all made - that is, stuff made of protons, neutrons and electrons - constitutes only 5 percent of the entire matter and energy in the universe. The nature of the other 95 percent remains unclear. What we do know is that it consists of two distinct types: “dark matter” and “dark energy.” Although we can’t see the dark matter, we are able to accurately measure its gravitational pull on regular visible matter, which slows down the expansion of the universe. Dark energy, in contrast - which constitutes roughly 65 percent of the stuff in the universe - also can’t be seen, but its gravitational effect is opposite to that of both dark and regular matter. It exerts a negative, or repulsive, force of gravity, thereby speeding up the expansion of the universe.

“The large amount of dark energy tends to accelerate the universe’s rate of expansion,” Hanany says, “thereby widening the distances between galaxies at an ever-increasing rate. If this process continues for several billions of years, Earth and our galaxy, the Milky Way, will be isolated in the expanse of the universe, while all other galaxies will have flown away to enormous distances, completely disappearing from view. The universe will seem dark and bleak.”

Hanany and his colleagues are currently focusing on the polarization of cosmic background radiation, hoping to obtain more information about the universe as it was a split second after the Big Bang. “It will be a fantastic sight - viewing the universe so close to its birth,” he says.

Iris Visoly-Fisher knew exactly what she wanted to work on when starting her Ph.D. - to follow up on a hunch that defects in a certain material used in solar cells would actually improve their performance.

But something was bugging her. She couldn’t understand why so few people were working on this topic. “It was a no-man’s-land,” she says. “It seemed clear that something was up, but there was virtually no literature on it.”

She soon found out why. The technical difficulties in examining this puzzle were daunting. To effectively tackle the problem, she would need to figure out how to zoom in on solar cell performance on the nanoscopic scale (equal to roughly one hundred-thousandth the width of a human hair).

An unexplained finding from years earlier was what had triggered this headache of a challenge. Most commercial solar cells are made of single-crystal semiconductors, such as silicon, Visoly-Fisher explains. But researchers had been looking around for alternative materials for a while, given silicon’s high manufacture costs. Then, nearly 15 years ago, a finding came up that was out of sync with all theoretical predictions. Certain solar cells made of polycrystalline (multi-grained) films were systematically outperforming their counterpart single-crystal cells.

Nobody understood why. Scientists working to improve solar cells had traditionally shied away from multi-grained films, despite their being significantly cheaper, since they contained numerous structural defects - a property believed to impair the light conversion process.

“In examining and reexamining the multi-grained films that had proven so successful, we could come up with only one key difference between them and the single-crystal films: the presence of a leading defect, known as the grain boundary defect,” says Visoly-Fisher, who performed the study under the guidance of Prof. David Cahen of the Institute’s Materials and Interfaces Department, in collaboration with Dr. Sidney Cohen of the Institute’s Chemical Research Support.

The team decided to take a closer look at these defects by studying the electrical properties of a single defect - in other words, the meeting point between two of these microscopic grains. And this is where their technical problems began.

They started out using an imaging technique based on atomic force microscopy (AFM). But given the Lilliputian scale of their study, it was impossible to determine that the results obtained were in fact due to the grain boundary defect, rather than merely being an experimental artifact.

Only after combining three different high-resolution imaging techniques, did they have an irrefutable answer: “The results were clear, and quite astounding: Contrary to earlier notions, grain boundary defects significantly enhance the efficiency of certain solar cells,” says Visoly-Fisher.

The finding, which was recently published in Advanced Materials, has to do with the basic principle underlying most solar cells. When light strikes the cell, the semiconductor within it serves as an “antenna,” absorbing the light energy, which releases electrons present in the semiconductor, allowing them to flow freely. These electrons are then harvested as an electric current for external use. As the Institute team has now shown, grain boundaries within solar cell films improve the light-to-electricity conversion because they provide a path where the freed electrons are efficiently collected and channeled on their way out.

“The grain boundaries essentially function as a freeway for electrons to exit, without traffic lights or roundabouts,” explains Cahen. “This finding offers a promising direction for improving solar cell performance while cutting production costs.”

And Visoly-Fisher adds: “There’s something immensely satisfying about solving a long-standing question in materials science by examining how the building blocks of the device work at the nano-scopic level. It’s like gaining entry to an almost imaginary world.”

Part of this study was performed in the labs of Prof. Israel Bar-Joseph of the Institute’s Condensed Matter Physics Department and Dr. Arie Ruzin of Tel Aviv University’s Department of Physical Electronics.

Sun “raycing”

On a sunny day, the sun beams approximately 1,000 watts of energy per square meter on our planet. Success in tapping this resource would transform the world’s energy industry, meeting all of our power demands for free. Solar cells are also environmentally sound, lacking any corrosive chemicals and giving off no pollutants.

More work is needed before solar technologies can become cost effective, but they are playing an increasingly important role, more than tripling their market between 1995 and 2000. Around the world, engineering students, scientists and industrialists are pushing ahead with new solar technologies - from self-sustaining solar homes to solar-powered cars. For instance, in a project launched by the U.S. Department of Energy, contractors have just put the finishing touches to a pilot $800,000 luxury home in Livermore, California, that produces its own electricity and even sells its surplus power to the local utility company. This trend has widespread parallels in Germany, where, motivated in part by the Chernobyl nuclear disaster, the government is pitching in to introduce solar-power systems to residential, public and commercial buildings.

Solar-powered car races are already a huge hit. In 2003, for example, university students from around the world participated in the World Solar Challenge across the vast Australian outback, pitting their self-designed cars, powered only by the sun, in a rigorous 3,000-km race.

Prof. Cahen’s research is supported by the Philip M. Klutznick Fund for Research; the Delores and Eugene M. Zemsky Weizmann-Johns Hopkins Research Program; the Minerva Stiftung Gesellschaft fuer die Forschung m.b.H. and the Wolfson Advanced Research Center. He is the incumbent of the Rowland Schaefer Professorial Chair in Energy Research.

When Itai Carmeli first came to his Ph.D. adviser with his results, he was gently told to get back to work. “I told him there was no such physics,” recalls a smiling Prof. Ron Naaman of the Institute’s Chemical Physics Department. “A year later he was back - with similar findings.”

Carmeli had been tinkering around with organic molecules, which he used to create extremely thin, single-layered films on a gold substrate. The surprise was that the films were behaving like a powerful magnet.

There are different types of magnets, Naaman explains, from the common fridge magnets we all played with as kids, which always display magnetic behavior; to temporary magnets such as paperclips and nails, which only work when exposed to a strong magnetic field; to magnets powered by an electric current. Nearly all of these contain one or more components with magnetic properties. The twist in our case was that the films lacked any magnetic materials.

In their study, recently published in Physical Review Letters and the Journal of Chemical Physics, the Institute team experimented with films made of three types of organic molecules. The molecules each had a positive and negative pole, and they were tightly packed, such that their negative poles faced the gold substrate, while their positive poles faced away. And this, says Naaman, might have been the trick: while opposite charges are known to attract, like charges repel, particularly when in close proximity on the surface of the film. The team - which included physicist Prof. Zeev Vager and materials scientists Prof. Shimon Reich and Dr. Gregory Leitus - believes that this repulsion force causes electrons to flow from the gold substrate to neutralize charged sites on the molecules in an attempt to stabilize the system. This extremely thin layer of flowing electrons in turn induces an electric current - forming a leading type of magnet dubbed an electromagnet (see box).

“We believe that the electrons are behaving as if in a co-op,” says Vager. “Electrons usually orbit in small circles, around individual molecules; but in this case they may be orbiting domains in the film containing hundreds of thousand of molecules, thus creating an electric current that transforms the system into a powerful magnet. Films of this sort might feature in electromagnets used in futuristic high-density discs and other electronics.”

Magnetic moments

Birds do it, bees do it, so do whales, salmon and, according to a new study, even Caribbean spiny lobsters - all use the Earth’s magnetic field as a navigating compass.

Magnetism was first discovered by the ancient Greeks and Chinese. Experimenting with the materials of their natural environment, they found that certain rare stones, called lodestones, attract small pieces of iron. Adding to their “magic,” these stones were found to always point in a north-south direction when suspended on a string. They quickly became invaluable to navigators, fortune-tellers and builders.

During the 13th century, French-man Pierre de Maricourt discovered that magnets had two magnetic poles - north and south - and in the 1600s, England’s Sir William Gilbert concluded that Earth itself was a giant magnet with north and south poles - which explains the wonder of animal migration treks.

The 1800s saw the first connection made between electricity and magnetism, when Danish physicist Hans Christian discovered that running an electric current through a wire creates a magnetic field - a phenomenon that quickly became known as electromagnetism. And today, this form of magnetism is everywhere - in the electric motors in refrigerators, washing machines and racecars; the read/write heads of discs and videotape players, and far more.

Prof. Naaman’s research is supported by the Fritz Haber Center for Physical Chemistry; the Ilse Katz Institute for Material Sciences and Magnetic Resonance Research; the Wolfson Advanced Research Center; the Philip M. Klutznick Fund for Research, Chicago, IL; and Dr. Pamela Scholl, Northbrook, IL. He is the incumbent of the Aryeh and Mintze Katzman Professorial Chair.