Spotlight - חוקרי הפקולטה משתפים

asymmetry image Light asymmetry explains the effect of nutrient enrichment on grassland diversity - Niv De Malach

One of the most ubiquitous patterns in plant ecology is species loss following nutrient enrichment.
A common explanation for this universal pattern is an increase in the size asymmetry of light partitioning (the degree to which large plants receive more light per unit biomass than smaller plants), which accelerates the rates of competitive exclusions. This ‘light asymmetry hypothesis’ has been confirmed by mathematical models, but has never been tested in natural communities due to the lack of appropriate methodology for measuring the size asymmetry of light partitioning in natural communities. Here, we use a novel approach for quantifying the asymmetry of light competition which is based on measurements of the vertical distribution of light below the canopy. Using our approach, we demonstrate that an increase in light asymmetry is the main
mechanism behind the negative effect of nutrient enrichment on species richness. Our results provide a possible explanation for one of the main sources of contemporary species loss in terrestrial plant communities.

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N-acetylcysteine amide (AD4) reduces cocaine-induced reinstatemen - small image N-acetylcysteine amide (AD4) reduces cocaine-induced reinstatement - Daphne Atlas

We prepared a non-toxic small-molecular weight compound, with combined anti-inflammatory, and metal chelating activities.  The new compound is the amide form of N-acetylcysteine (NAC).   NAC itself is being used in the clinic for over 40 years but displays a relatively low efficacy.

The amide form of NAC, NAC-amide, is called AD4 or NACA, and is highly effective because it is both water-soluble and crosses cell membranes.  A large number of in vivo and in vitro studies have shown that AD4 is significantly more effective than NAC.

In this new study, AD4 (NAC-amide) was examined in intravenous cocaine self-administration and extinction/reinstatement procedures in rats.

We investigated the behavioral effects of AD4 in the olfactory bulbectomized (OBX) rats, considered an animal model of depression. We also tested rats injected with AD4 or NAC during 10-daily extinction training sessions to examine subsequent cocaine seeking.

We found that AD4 is highly effective in reducing cocaine-induced reinstatement in rats with preexisting depression. It is more potent than NAC in reducing cocaine-induced reinstatement in rats with preexisting depression

AD4 is very effective because it was also shown to inhibit metalloproteinase 9 (MMP-9), which is required for cocaine relapse and relapse-associated synaptic plasticity

AD4 treatment represents a new approach to treat substance-use disorders through affecting the glutaminergic pathway aimed at improving the dopaminergic system.  In addition AD4 helps the cells to better manage drug-induced changes through increasing the reductive state and lowering inflammatory insults.

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Chart image that compairs Tolerance, Resistance and Survival Physicists unveil how bacteria can evolve fast towards antibiotic resistance - Prof. Nathalie Balaban

A new research appearing this week in SCIENCE, led by PhD student Irit Levin-Reisman in Prof. Nathalie Balaban's lab, show that bacteria first evolve to "sleep" for most of the antibiotic treatment, and then this "sleeping mode" not only transiently protected them from the lethal action of the drug, but also actually worked as a stepping stone for the later acquisition of resistance factors. The experiments were performed by a team of physicists, who developed a theoretical model and computer simulations that enabled a deep understanding of the reason behind the fast evolution of resistance that was observed. These findings may have important implications for the development of new antibiotics, as they suggest news way to delay the evolution of resistance, one of the burning health issues today. It is important to note that these dormant bacteria would go undetected in the current tests done in the clinic. In order to bridge this gap, a complementary study from the same lab, and led by Scholar-Teacher Dr. Orit Gefen, demonstrates a new and easy method for the detection of dormant bacteria in the clinical setting and may help avoid the evolution of resistance in real time.
Irit Levin-Reisman et al., Science (2017)
Orit Gefen et al. Scientific Reports (2017)

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 neutron stars Does a merger of two neutron stars leads to the formation of a magnetar? - Assaf Horesh

The recent discovery of gravitational waves by LIGO opens a new era in astrophysics. While the event discovered by LIGO originated from the merger of two black holes, LIGO is also capable and is expected to discover mergers of Neutron stars. In a Neutron star merger, a small amount of material will be ejected at velocities of about 30,000 km/s. This material will be radioactively heated and hence will emit a weak and brief (1 day to a weak) optical/infra-red signal, named macronovae. Such a macronovae signal was first detected only a few years ago as the counterpart of short gamma-ray bursts (which are believed to also originate from compact binary mergers). The same material that is responsible for the macro novae signal, will also interact with environment, create a shockwave, and lead to radio emission. It is possible that in the merger process a magnetar will form (and not necessarily a black hole). A magnetar is a fast rotating neutron star (1 ms period) with a large magnetic field (> 10^15 Gauss). In this case, the magnetar will deposit its energy into the ejecta and will drive a much stronger shockwave, thus increasing, by at least an order of magnitude, the radio emission. We recently observed two macronoave candidates, in search for this radio emission. Our results suggest that at least in the events that we observed, no standard magnetar was formed, unless the magnetar had different properties than theory predicts. Following this results, we are conducting further radio observations of similar events, in an attempt to better characterize them and to unveil their nature.


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Thumbnail of supernova A Young Supernova Reveals the Secrets of a Dying Star - Dr. Assaf Horesh

Massive stars end their lives in an explosion called supernova. Understanding the last stages of evolution in a star life, leading to a supernova, and understanding the explosion itself, are some of the leading questions in astrophysics today. Not knowing when and where a supernova will occur makes it even harder to study this phenomena. Nowadays, we have the capability to discover many supernovae a night thanks to many dedicated experiments. Our detection capability has improved recently and we can now discover supernovae only a few hours after explosion!

Supernova SN2013fs was discovered by the Palomar Transient Factory project three hours after explosion. The early discovery allowed us to perform followup observations with more advanced telescopes such as the Keck telescope, which provided several optical spectra over a few hours after detection. These spectra revealed the existence of dense gas in the close vicinity around the supernova (10^15 cm) that was ionized by the flash from the supernova explosion. The spectral signatures of this gas have disappeared a few days after the discovery, leading to the conclusion that there was a dense massive shell of gas around the supernova which was swept away by the stellar material that was ejected in the explosion. Late-time radio observations support this conclusion.

Massive stars loose mass along their lives thus enriching their surroundings with low density gas. Discovering a dense shell of gas so close to the star that exploded suggests that massive stars go through major dynamical processes which make the star loose a lot of mass in a short time, during the last year of their lives. These processes are still not well understood and there are several theories explaining them. Understanding these processes is critical to our understanding of the processes inside dying stars which lead to supernova explosions.
The results of this research have been recently published in Nature (the research was performed by an international team of researchers led by Dr. Ofer Yaron from the Weizmann Institute and in collaboration with Dr. Assaf Horesh from the Hebrew University)

Single Colloidal Nanopracticle - thumbnail Scientists Demonstrate a Compact, Efficient Single Photon Source That Can Operate at Ambient Temperatures On a Chip - Prof. Ronen Rapaport

Highly directional single photon source concept is expected to lead to a significant progress in producing compact, cheap, and efficient sources of quantum information bits for future applications

Quantum information science and technology has emerged as a new paradigm for dramatically faster computation and secure communication in the 21st century. At the heart of any quantum system is the most basic building block, the quantum bit or qbit, which carries the quantum information that can be transferred and processed (this is the quantum analogue of the bit used in current information systems). The most promising carrier qbit for ultimately fast, long distance quantum information transfer is the photon, the quantum unit of light.

The challenge facing scientists is to produce artificial sources of photons for various quantum information tasks. One of the biggest challenges is the development of efficient, scalable photon sources that can be mounted on a chip and operate at room temperature. Most sources used in labs today have to be very cold (at the temperature of liquid Helium, about -270C), which requires large and expensive refrigerators. Many sources also emit photons in undefined directions, making efficient collection a hard problem.

Now, a team of scientists from the Hebrew University of Jerusalem has demonstrated an efficient and compact single photon source that can operate on a chip at ambient temperatures. Using tiny nanocrystals made of semiconducting materials, the scientists developed a method in which a single nanocrystal can be accurately positioned on top of a specially designed and carefully fabricated nano-antenna.

In the same way large antennas on rooftops direct emission of classical radio waves for cellular and satellite transmissions, the nano-antenna efficiently directed the single photons emitted from the nanocrystals into a well-defined direction in space. This combined nanocrystals-nanoantenna device was able to produce a highly directional stream of single photons all flying to the same direction with a record low divergence angle. These photons were then collected with a very simple optical setup, and sent to be detected and analyzed using single photon detectors.

The team demonstrated that this hybrid device enhances the collection efficiency of single photons by more than a factor of 10 compared to a single nanocrystal without the antenna, without the need for complex and bulky optical collection systems used in many other experiments. Experimental results show that almost 40% of the photons are easily collected with a very simple optical apparatus, and over 20% of the photons are emitted into a very low numerical aperture, a 20-fold improvement over a freestanding quantum dot, and with a probability of more than 70% for a single photon emission. The single photon purity is limited only by emission from the metal, an obstacle that can be bypassed with careful design and fabrication.

The antennas were fabricated using simple metallic and dielectric layers using methods that are compatible with current industrial fabrication technologies, and many such devices can be fabricated densely on one small chip. The team is now working on a new generation of improved devices that will allow deterministic production of single photons straight from the chip into optical fibers, without any additional optical components, with a near unity efficiency.

"This research paves a promising route for a high purity, high efficiency, on-chip single photon source operating at room temperature, a concept that can be extended to many types of quantum emitters. A highly directional single photon source could lead to a significant progress in producing compact, cheap, and efficient sources of quantum information bits for future quantum technological applications", said Prof. Ronen Rapaport, of the Racah Institute of Physics, The Department of Applied Physics, and the Center of Nanoscience and Nanotechnology at the Hebrew University of Jerusalem.

The Hebrew University of Jerusalem is Israel’s leading academic and research institution, producing one-third of all civilian research in Israel. For more information, visit

FUNDING: The research was supported in parts by the Einstein Foundation Berlin; the U.S. Department of Energy: Office of Basic Energy Sciences, Division of Materials Sciences and Engineering; the European Cooperation in Science and Technology through COST Action MP1302 Nanospectroscopy;  and by the Ministry of Science and Technology, Israel.

REFERENCE: Highly Directional Room-Temperature Single Photon Device. Nitzan Livneh, Moshe G. Harats, Daniel Istrati, Hagai S. Eisenberg, and Ronen Rapaport. Nano Lett., 2016, 16 (4), pp 2527–2532. DOI: 10.1021/acs.nanolett.6b00082.

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Advnaced Imaging - small picture "The Marker" article on the research at the Advnaced Imaging Lab of the Applied Physics Department - Dr. Uri Katz

A special article on the research at the Advanced Imaging Lab in the Hebrew University Applied Physics Department, led by Dr. Ori Katz, was published in "The Marker" magazine
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A novel technique for endoscopic imaging through multicore fibers - thumbnail A novel technique for endoscopic imaging through multicore fibers - Dr. Uri Katz

Researchers from the Hebrew University Applied Physics Department in collaborations with researchers from the Weizmann Institute and from Paris, France, have developed a novel technique for endoscopic imaging through multicore fibers, using no lenses or optical elements besides the fiber. The technique is based on exploiting inherent correlations of coherent light propagating in such fibers.


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Rota's basis conjecture - thumbnail Solution of the Rota conjecture - Karim Adiprasito

 We recently solved the so-called Rota conjecture, a 45 year old problem in  combinatorics that has baffled generations of researchers. The methods developped surprised even more, as they extended classical results of algebraic geometry to purely combinatorial settings
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In the light of a neutron star, astronomers have found evidence for a quantum effect discovered in the 1930s. - smal image The discovery of weird quantum effects in the vacuum around neutron stars - Nir Shaviv

A prediction made by Prof. Nir Shaviv from the Racah Institute of Physics at the Hebrew University and Prof. Jeremy Heyl from the University of British Columbia in Vancouver Canada is reaffirmed through the measurement of polarized light from a neutron star. As a result of the very strong magnetic fields around neutron stars, the light rays can interact with the virtual electrons in the Vacuum. This interaction gives rise to very strange effects, the evidence of which was only recently seen for the first time.


Unique properties of Human neurons - small image Unique properties of Human neurons - Idan Segev

A new modeling study shows that human cortical neurons have distinctive membrane properties, suggesting important implications for signal processing in the human neocortex, The theoretical results were validated in experiments perfumed in fresh human cortex following brain operations at the Fry University Hospital in Amsterdam. The study was performed by Guy Eyal, a Ph.D. student of Prof. Idan Segev at the Department of Neurobiology the Hebrew University of Jerusalem.

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Accessing Human Selenoproteins through Chemical Protein Synthesis - small photo Accessing Human Selenoproteins through Chemical Protein Synthesis - Norman Metanis

The human body contains 25 selenoproteins. This is a small family of proteins which contain in their sequence the twenty-first encoded amino acid, selenocysteine. About a dozen of these proteins remain functionally uncharacterized or poorly studied. The bottleneck in studying selenoproteins is the challenges in accessing these proteins using traditional recombinant expressions, which have prevented biological characterization thus far. Chemical protein synthesis has the potential to overcome these hurdles. In a recent seminal paper published in the journal Chemical Science, our group report the first total chemical syntheses of two human selenoproteins, selenoprotein M (SELM) and selenoprotein W (SELW). The synthesis of the more challenging protein SELM was enabled using recent advances in the field of selenocysteine chemistry, which we mastered in our lab. This approach allow the preparation of selenoproteins in milligram quantities and in homogenous form, which should open new horizons for future studies to pursue a fuller biological understanding of their role in health and disease.

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Ubiquitin Accumulation on Disease Associated Protein Aggregates Is Correlated with Nuclear Ubiquitin Depletion, Histone De-Ubiquitination and Impaired DNA Damage Response A possible link between neurodegeneration associated aggregates and cellular aging - Prof. Michael Brandeis

Neurodegenerative diseases, like Parkinson and Alzheimer are associated with cellular protein aggregation. A method to follow aggregation in living cultured cells in real time was developed in the laboratory of Prof. Michael Brandeis of the Department of Genetics of the Life Science Institute. This method enables to study the effect of aggregates on cellular proteins and organelles. Ubiquitin is a small protein playing an essential role in protein degradation and DNA damage repair. The omnipresence of ubiquitin in disease associated aggregates is well established. This method enabled, for the first time to characterize the dynamics ubiquitin accumulation on aggregates. Research by the master students Adi Ben Yehuda and Marwa Risheq revealed that this accumulation leads to the depletion of nuclear ubiquitin. Given the role of ubiquitin for DNA repair, this observation suggested that aggregates compromises genome repair. Such a defect is particularly significant in brain neurons that suffer from extensive DNA damage. Ofra Novoplansky, another student in the lab, showed that aggregates puncture the nuclear lamina thereby disrupting the nuclear cytoplasmic compartmentalization. In contrast to most cells in the body, brain neurons hardly regenerate throughout life, their aging is exceedingly slow and their number does hardly decline in old age. Impaired DNA repair, disruption of the nuclear lamina, as well as the reduced capacity to degrade proteins, discovered in a previous research done by this approach, are all well-established hallmarks of aging. The observed correlation between protein aggregation and the appearance of these hallmarks suggests that aggregates cause premature neuron aging and could lead to neurodegeneration. It is important to stress that these are preliminary observations and that their possible application for treating neurodegeneration lay still a far way ahead. This research, published last week in PlosONE, was funded by the Israeli Ministry of Health and the Israeli Science Foundation.

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Comics image - thumbnail One out of ten most promising researchers for 2016 - TheMarker - Dan Cohen

A doctoral student in the Department of Physics at the Hebrew University (32) breakthrough PhD research of Dan Cohen will help realize one of the most important questions in nuclear physics of today: What is the size of particles called protons, which are in the nucleus of every atom. Various experiments to measure the radius of the proton, some of them in recent years have yielded different results without a satisfactory explanation; the trial of Cohen, led by Prof. Guy Ron, offering innovative technique and guarantees. Cohen is part of an international group which integrate and work at the particle accelerator PSI, Switzerland. this year he is expected to complete at the Hebrew university the construction of his special detector, which is a screen like detector, the two types of particles will scatter on it: electrons are elementary particles in nature, and muons are similar to electrons but heavier than them. the experiment will be carried out at a particle accelerator in Switzerland, which is the only site in the world where this can be done. the accelerator will shoot at the protons the two particle types (separately) from the information collected on the interaction between the protons and the particles using their dispersion on the detector, it will be possible to calculate the size of the proton. One can imagine this ball doused in water and then with oil, and from the different distribution of the oil and water drops splashing from the ball, we can calculate its size. The experiment is expected to be completed within three years. Cohen, who dreamed of being an astronaut from an early age, realized that the way to realize the dream goes through learning sciences. He is alumnus of Space Studies Program 2014, from the International Space University and volunteer as the head of landing site selection team at SpaceIL. This is a non-profit organization founded in 2011 by three young Israeli engineers, and aims to launch the first Israeli spaceship on the moon, and a way to inspire the next generation of scientists and engineers. After completing his doctorate one can assume that Cohen will do postdoctoral at the United States which leads the field, and then he wants to come back and to be a researcher at Israel. The dream of being an astronaut is still vivid in his blood.

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thumnail Accessing human selenoproteins through chemical protein synthesis - Norman Metanis

The research group of Dr. Norman Metanis, from the Institute of Chemistry, specializes in organic and bioorganic chemistry and has recently published an article in Chemical Science, in which they describe for the first time a method to access human selenoproteins by total chemical protein synthesis. The human body contains 25 selenoproteins, which contain in their sequence the twenty-first encoded amino acid, selenocysteine. About a dozen of these proteins remain functionally uncharacterized or poorly studied. Challenges in accessing these selenoproteins using traditional recombinant expressions have prevented biological characterization thus far. The Metanis group reported the total chemical syntheses of two human selenoproteins, selenoprotein M (SELM) and selenoprotein W (SELW). The synthesis of the more challenging protein SELM, which is longer, was enabled using recent advances in the field of selenocysteine chemistry that was developed in the lab. This approach allows the preparation of selenoproteins in milligram quantities and in homogenous form, which should open new horizons for future studies to pursue a fuller biological understanding of their role in health and disease, which is currently ongoing in the Metanis group.

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3D printing - small image 3D printing of highly stretchable UV curable elastomers - Dr. Michael LAyani

Elastomeric structures show a lot of interest in different research fields such as soft robotics, flexible electronics, and smart biomedical devices which require soft and deformable material properties. However, to date, the most widely used materials are silicon rubber based for e.g. PDMS. The fabrication methods using these materials are limited to traditional ways, such as cutting, molding and casting, thus constrains the design freedom and geometric complexity. In order to enrich the design and fabrication flexibility, researchers attempted to use 3D printing techniques, especially the UV curing based 3D printing techniques, to fabricate elastomeric 3D objects. Nevertheless, most of the commercially available UV curable thus 3D printable elastomers break at less than 200 %, which is insufficient to many applications.
In the recent publication published in the prestigious journal Advanced Materials, researchers from the group of Prof. Shlomo Magdassi, led by Dr. Dinesh Patel and Dr. Michael Layani showed the development of a family of highly stretchable and UV curable (SUV) elastomers that can be stretched by up to 1100%, and are suitable to Digital Light Processing (DLP) and other UV curing based 3D printing techniques. This enabled the researchers to print diverse structures such as a deformable 3D isotropic truss, a deformable 3D negative Poisson’s ratio structure, 3D printed soft actuators and stretchable grippers activated by pressure, Bucky ball electronic switches, and even a 3D printed balloon, which demonstrate the ink's elastomer advantage of high stretchability and compatibility with DLP printing technique. The research was performed in collaboration with Singapore University of Technology and Design (SUTD). We believe the SUV elastomers will significantly enhance the capability of the UV curing based 3D printing of fabricating soft and deformable 3D structures and devices including soft actuators and robots, flexible electronics, acoustic metamaterials, and many other applications.

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Habitability of exoplanets Habitability of exoplanets - Dr. Amri Wandel

The recent detection of small planets within the Habitable Zone of Proxima Centauri and many other M-dwarf stars makes such planets prime candidates to look for life. In a recent article Joseph Gale and Amri Wandel discuss the potential of planets orbiting red dwarf stars to support photosynthesis and complex life. They combine the latest findings from the Kepler space telescope on the number of Earth-sized planets, with calculations showing that the appearance of life clement conditions on planets of red dwarf stars is possible and more probable than previously thought. In a recently submitted paper Wandel argues that Proxima b and other planets in the Habitable Zone of M dwarfs may support liquid water for a wide range of properties, including their atmosphere, irradiation and heat redistribution. This work also suggest a method that could give a quantitative estimation of the abundance of life on exoplanets, using the future telescopes JWST and TESS, planned for launch by 2018.


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stratosphere - thumbnail Stratospheric variability contributed to and sustained the recent hiatus in Eurasian winter warming - Dr. Chaim Garfinkel

The rate of surface warming over the most recent 15 or so years has been considerably less than that since the mid-20th century - the so-called hiatus. This effect is most pronounced over Eurasia in wintertime, where a series of cold winters has led some to cast doubt on the basic science behind anthropogenic climate change. The cause of this cooling is still not understood. In this paper, we demonstrate that the recent Eurasian cooling was caused, at least in part, by stratospheric processes. Similar hiatus events could happen again even in a future with high GHG concentrations.

Accepted by Geophysical Research Letters.


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Regeneration Vs. Tail - thumbnail Heads or tails? The whole body regeneration scheme of the sea-anemone Nematostella. - Dr. Uri Gat

Whole-body regeneration is the ability of some animals to reconstruct entire body parts after major damage such as cutting into two fragments. This may seem incredible to us but several very different animals are able to perform this feat quite easily, a phenomenon that has attracted the interest of naturalists and scientists for ages. In our lab we are studying the whole-body regeneration process of a simple animal called the sea anemone Nematostella. This animal belongs to cnidarians (e.g: medusas, corals) and has a remarkable ability to regenerate even after cutting it into several parts. Surprisingly the genome sequence of Nematostella revealed a large extent of genes and even genome segments that are very similar to those of man, especially genes that function in embryonic development.
To better understand this mystery we have explored the genetic program, in which after bisection in the middle, the "tail" half reconstructs the head and the "head" part rebuilds the tail. In this project we have charted the genes that are induced at different time points along the regeneration process and compared their action in the head versus the tail forming parts. This screen identified many genes that are involved in the formation of the basic body axis in the embryonic development stage and also discovered new genes that may be specific to the regeneration program.
In this research we have also characterized the main genetic networks that are involved in regeneration and we now know more about which gene tools are responsible for the head and tail reconstruction jobs as well as their logic of operation. A large proportion of these genes are common to us, and thus this information can lead in the future to better wound healing treatments in people and may even allow some organ repair after major injuries.

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