FLUORESCENCE AND CIRCULAR DICHROISM STUDIES ON THE PHYCOERYTHROCYANINS FROM THE CYANOBACTERIUM

Two phycoerythrocyanin (PEC) fractions have been obtained from the phycobilisomes of the cyanobac-terium Westiellopsis prolifica ARM 365. They have been characterized by absorption, fluorescence and circular dichroism spectroscopy. One of them is spectroscopically similar to a PEC trimer known from other organisms. Whereas efficient energy transfer from its violin (α-84) to the cyanin (β-84, 155) chromophores is efficient in the trimer (αβ it is impeded after dissociation to the monomer (α,β). A second fraction of PEC which we earlier termed PEC(X) (Maruthi Sai et al., Photochem. Photobiol. 55,119–124, 1992), exhibited the spectral properties similar to that of the α-subunit of PEC from Mastigocladus laminosus. With this highly photoactive fraction, the circular dichroism spectra of the violobilin chromophore in both photoreversible states were obtained

PHYCOERYTHROCYANINS FROM Westiellopsis prolifica AND Nostoc rivulare: CHARACTERIZATION OF THE PHYCOVIOLOBILIN CHROMOPHORE IN BOTH STATES

Phycoerythrocyanin or fractions enriched in it have been isolated from the filamentous cyanobacteria, Westiellopsis prolifica ARM 365 and Nostoc rivulare ARM 212. Both show the photoreversible photochromism (difference maxima at 503 and 570 nm) characteristic of this pigment, which is related to the phycoviolobilin chromophore on the α-subunit. Native phycoerythrocyanin and its β-subunit show little if any reversible photochemistry in the 600–620 nm region, where the phycocyanobilin chromophores absorb maximally. Instead the phycocyanobilin chromophores are bleached irreversibly. At the same time, the data show that reversible photochemistry is a useful analytical tool to detect phycoerythrocyanin in cyanobacterial extracts. Fluorescence measurements indicate that: (i) the 510 nm absorbing isomer of the violobilin chromophore has only little fluorescence; and (ii) the energy transfer from the violobilin chromophores to the cyanin chromophores is efficient only in the 570 nm form

A Comparison of Phycocyanins from Three Different Species of Cyanobacteria Employing Resonance-Enhanced Coherent Anti-Stokes Raman Spectroscopy

Resonance-enhanced coherent anti-Stokes Raman spectra are recorded for monomers and trimers of phycocyanin from three different cyanobacteria: Westiellopsis prolifica, Mastigocladus laminosus and Spirulina platensis. It is shown that upon aggregation from monomer to trimer the electronic structures of both the α84 and β84 chromophores are changed. The spectra of the trimers originating from S. platensis and M. laminosus are very similar to each other, but distinctly different from the spectrum of W. prolifica

Estimation of Buttiker-Landauer traversal time based on the visibility of transmission current

We present a proposal for the estimation of B\"uttiker-Landauer traversal time based on the visibility of transmission current. We analyze the tunneling phenomena with a time-dependent potential and obtain the time-dependent transmission current. We found that the visibility is directly connected to the traversal time. Furthermore, this result is valid not only for rectangular potential barrier but also for general form of potential to which the WKB approximation is applicable . We compared these results with the numerical values obtained from the simulation of Nelson's quantum mechanics. Both of them fit together and it shows our method is very effective to measure experimentally the traversal time.Comment: 12 pages, REVTeX, including 7 eps figure

On Free-Electron Laser Growing Modes and their Bandwidth

Free-electron lasers play an increasing role in science, from generating unique femtosecond X- ray pulses for single short recording of the protein structures to amplifying feeble interactions in advanced cooling systems for high-energy hadron colliders. While modern Free-electron laser codes can describe their amplification mechanism, a deep analytical understanding of the mechanism is of extreme importance for a number of applications. Mode competition, their growth rates and amplification bandwidth are among the most important parameters of a free-electron laser. A dispersion relation, which defines these important characteristics, can be solved analytically only for a very few simple cases. In this letter we show that for a typical bell-shape energy distribution in electron beam there is no more that one growing mode. We also derive an analytical expression which determines the bandwidth of the free-electron laser.Comment: 4 pages, submitted to PR

Influence of chromophores on quarternary structure of phycobiliproteins from the cyanobacterium, Mastigocladus laminosus

Chromophores of C-phycocyanin and phycoerythrο-cyanin have been chemically modified by reduction to rubins , bleaching , photoisomerization , or perturbation with bulky substituents. Pigments containing modified chromophores, or hybrids containing modified and unmodified chromophores in individual protomers have been prepared. All modifications inhibit the association of the (aß)-protomers of these pigments to higher aggregates. The results demonstrate a pronounced effect of the state of the chromophores on biliprotein quaternary structure. It may be important in phycobi1isome assembly , and also in the dual function of biliproteins as (i) antenna pigments for photosynthesis and (ii) reaction centers for photomor-phogenesis

Shared visiting in Equator city

In this paper we describe an infrastructure and prototype system for sharing of visiting experiences across multiple media. The prototype supports synchronous co-visiting by physical and digital visitors, with digital access via either the World Wide Web or 3-dimensional graphics

TWO DIFFERENT TYPES OF PHOTOCHEMISTRY IN PHYCOERYTHROCYANIN α-SUBUNIT

The photochemical activities of phycoerythrocyanin α-subunits from Mastigocladus laminosus separated by isoelectric focusing were tested by irradiating at 500, 550, 577 and 600 nm. Two types of photoreversible photochromic responses have been characterized by absorption and absorption difference spectroscopy. Type I is the well-known absorption shift from 571 to 506 nm. Type II is a new response characterized by a line-broadening of the 570 nm absorption

It's more than just money: The real-world harms from ransomware attacks

As cyber-attacks continue to increase in frequency and sophistication, organisations must be better prepared to face the reality of an incident. Any organisational plan that intends to be successful at managing security risks must clearly understand the harm (i.e., negative impact) and the various parties affected in the aftermath of an attack. To this end, this article conducts a novel exploration into the multitude of real-world harms that can arise from cyber-attacks, with a particular focus on ransomware incidents given their current prominence. This exploration also leads to the proposal of a new, robust methodology for modelling harms from such incidents. We draw on publicly-available case data on high-profile ransomware incidents to examine the types of harm that emerge at various stages after a ransomware attack and how harms (e.g., an offline enterprise server) may trigger other negative, potentially more substantial impacts for stakeholders (e.g., the inability for a customer to access their social welfare benefits or bank account). Prominent findings from our analysis include the identification of a notable set of social/human harms beyond the business itself (and beyond the financial payment of a ransom) and a complex web of harms that emerge after attacks regardless of the industry sector. We also observed that deciphering the full extent and sequence of harms can be a challenging undertaking because of the lack of complete data available. This paper consequently argues for more transparency on ransomware harms, as it would lead to a better understanding of the realities of these incidents to the benefit of organisations and society more generally.Comment: 17th International Symposium on Human Aspects of Information Security & Assurance (HAISA 2023

Cyber Insurance and the Cyber Security Challenge

Governments and businesses are struggling to cope with the scale and complexity of managing cyber risk. Over the last year, remote working, rapid digitalisation and the need for increased connectivity have emphasised the cyber security challenge. As the pursuit of approaches to prevent, mitigate and recover from malicious cyber activity has progressed, one tool that has gained traction is cyber insurance. If it can follow the path of other insurance classes, it could play a significant role in managing digital risk. This paper explores whether cyber insurance can incentivise better cyber security practices among policyholders. It finds that the shortcomings of cyber insurance mean that its contribution to improving cyber security practices is more limited than policymakers and businesses might hope. Although several means by which cyber insurance can incentivise better cyber security practices are identified, they have significant limitations. Interviewees from across government, industry and business consistently stated that the positive effects of cyber insurance on cyber security have yet to fully materialise. While some mature insurers are moving in the right direction, cyber insurance as a whole is still struggling to move from theory into practice when it comes to incentivising cyber security. If this is to change, the insurance industry must overcome significant challenges. One is the competitiveness of the nascent cyber insurance market over the last two decades. Most of the market has used neither carrots (financial incentives) nor sticks (security obligations) to improve the cyber security practices of policyholders. The industry is also struggling to collect and share reliable cyber risk data that can inform underwriting and risk modelling. The difficulties inherent in understanding cyber risk, which is anthropogenic and systemic, mean insurers and reinsurers are unable to accurately quantify its causes and effects. This limits insurers’ ability to accurately assess an organisation’s risk profile or security practices and price policy premiums accordingly. The spectre of systemic incidents such as NotPetya1 and SolarWinds2 has also limited the availability of capital for cyber insurance markets. However, the most pressing challenge currently facing the industry is ransomware. Although it is a societal problem, cyber insurers have received considerable criticism for facilitating ransom payments to cybercriminals. These add fuel to the fire by incentivising cybercriminals’ engagement in ransomware operations and enabling existing operators to invest in and expand their capabilities. Growing losses from ransomware attacks have also emphasised that the current reality is not sustainable for insurers either. To overcome these challenges and champion the positive effects of cyber insurance, this paper calls for a series of interventions from government and industry. Some in the industry favour allowing the market to mature on its own, but it will not be possible to rely on changing market forces alone. To date, the UK government has taken a light-touch approach to the cyber insurance industry. With the market undergoing changes amid growing losses, more coordinated action by government and regulators is necessary to help the industry reach its full potential. The interventions recommended here are still relatively light, and reflect the fact that cyber insurance is only a potential incentive for managing societal cyber risk. They include: developing guidance for minimum security standards for underwriting; expanding data collection and data sharing; mandating cyber insurance for government suppliers; and creating a new collaborative approach between insurers and intelligence and law enforcement agencies around ransomware. Finally, although a well-functioning cyber insurance industry could improve cyber security practices on a societal scale, it is not a silver bullet for the cyber security challenge. It is important to remember that the primary purpose of cyber insurance is not to improve cyber security, but to transfer residual risk. As such, it should be one of many tools that governments and businesses can draw on to manage cyber risk more effectively