Cancer stem cells modulate patterns and processes of evolution in cancers

The clonal evolution (CE) model and the cancer stem cell (CSC) model are two independent models of cancers, yet recent data shows intersections between the two models. This article explores the impacts of the CSC model on the CE model. I show that CSC restriction, which depends on CSC frequency in cancer cell populations and on the probability of dedifferentiation of cancer non-stem cells (non-CSC) into CSCs, can favor or impede some patterns of evolution (linear or branched evolution) and some processes of evolution (drift, evolution by natural selection, complex adaptations). Taking CSC restriction into account for the CE model thus has implications for the way in which we understand the patterns and processes of evolution, and can also provide new leads for therapeutic interventions

The risk–reward nexus: a qualitative analysis of public–private partnerships for investments in innovation in Brazil

Governments throughout the world are confronted with new challenges, in particular having to reconcile economic growth, sustainability and social inclusion. Tackling these issues requires new forms of collaboration between public and private actors. As such, how can public–private partnerships be effective? This research addresses the emergence of the state’s active role as a risk-taker and co-investor in technological innovation. The analysis undertaken considers policy issues that arise from public–private partnerships, by focusing on how public actors may directly appropriate financial rewards. From a perspective that views innovation policy as creating markets, experimentation is crucial for shaping equitable partnerships and strengthening the entrepreneurial role of the state. Furthermore, purposeful state action can influence the institutional frameworks within which these partnerships unfold, and favour the realisation of socially desirable policy goals. The interplay between the two – experimentation with partnerships and changes in the institutional environment – is investigated in three papers that are presented as chapters within the thesis. In Chapter 1 a framework for studying public–private partnerships for investments in innovation is developed. By highlighting the legal dimension of the role of the state in institutional change, the framework includes essential tools that public actors could use for negotiating more equitable reward distribution with business. In chapters 2 and 3 concrete attempts to build investment partnerships in Brazil are examined, focusing on the recent revival of active and explicit industrial policies in the country. Chapter 2 is a comparative analysis of two R&D programmes, oriented towards biofuels and health, which leads to an appraisal of their preliminary outcomes, viewed through the risk–reward nexus lens. Chapter 3 comprises an in-depth case study in the qualities (attributes and functions) of the contracts that enable public actors to appropriate financial rewards of high-risk investments. Viewed as a whole, these three chapters contribute to the understanding of the legitimation processes that underlie the role of the state as an investor, by offering a nuanced appreciation of the limits, tensions, possibilities and tools for building effective public–private partnerships. The theoretical and practical insights from this thesis should benefit the design, implementation and assessment of innovation policies geared to tackling contemporary challenges in Brazil and elsewhere

Multi-mode and long-lived quantum correlations between photons and spins in a crystal

The realization of quantum networks and quantum repeaters remains an outstanding challenge in quantum communication. These rely on entanglement of remote matter systems, which in turn requires creation of quantum correlations between a single photon and a matter system. A practical way to establish such correlations is via spontaneous Raman scattering in atomic ensembles, known as the DLCZ scheme. However, time multiplexing is inherently difficult using this method, which leads to low communication rates even in theory. Moreover, it is desirable to find solid-state ensembles where such matter-photon correlations could be generated. Here we demonstrate quantum correlations between a single photon and a spin excitation in up to 12 temporal modes, in a $^{151}$Eu$^{3+}$ doped Y$_2$SiO$_5$ crystal, using a novel DLCZ approach that is inherently multimode. After a storage time of 1 ms, the spin excitation is converted into a second photon. The quantum correlation of the generated photon pair is verified by violating a Cauchy - Schwarz inequality. Our results show that solid-state rare-earth crystals could be used to generate remote multi-mode entanglement, an important resource for future quantum networks

High precision measurement of the Dzyaloshinsky-Moriya interaction between two rare-earth ions in a solid

We report on a direct measurement of the pair-wise anti-symmetric exchange interaction, known as the Dzyaloshinsky-Moriya interaction (DMI), in a Nd3+-doped YVO4 crystal. To this end we introduce a broadband electron spin resonance technique coupled with an optical detection scheme which selectively detects only one Nd3+-Nd3+ pair. Using this technique we can fully determine the spin-spin coupling tensor, allowing us to experimentally determine both the strength and direction of the DMI vector. We believe that this ability to fully determine the interaction Hamiltonian is of interest for studying the numerous magnetic phenomena where the DMI interaction is of fundamental importance, including multiferroics. We also detect a singlet-triplet transition within the pair, with a highly suppressed magnetic-field dependence, which suggests that such systems could form singlet-triplet qubits with long coherence times for quantum information applications

Multiplexed on-demand storage of polarization qubits in a crystal

A long-lived and multimode quantum memory is a key component needed for the development of quantum communication. Here we present temporally multiplexed storage of 5 photonic polarization qubits encoded onto weak coherent states in a rare-earth-ion doped crystal. Using spin refocusing techniques we can preserve the qubits for more than half a millisecond. The temporal multiplexing allows us to increase the effective rate of the experiment by a factor of 5, which emphasizes the importance of multimode storage for quantum communication. The fidelity upon retrieval is higher than the maximum classical fidelity achievable with qubits encoded onto single photons and we show that the memory fidelity is mainly limited by the memory signal-to-noise ratio. These results show the viability and versatility of long-lived, multimode quantum memories based on rare-earth-ion doped crystals

Cavity-enhanced storage in an optical spin-wave memory

We report on the experimental demonstration of an optical spin-wave memory, based on the atomic frequency comb (AFC) scheme, where the storage efficiency is strongly enhanced by an optical cavity. The cavity is of low finesse, but operated in an impedance matching regime to achieve high absorption in our intrinsically low-absorbing Eu3+:Y2SiO5 crystal. For storage of optical pulses as an optical excitation (AFC echoes), we reach efficiencies of 53% and 28% for 2 and 10 microseconds delays, respectively. For a complete AFC spin-wave memory we reach an efficiency of 12%, including spin-wave dephasing, which is a 12-fold increase with respect to previous results in this material. This result is an important step towards the goal of making efficient and long-lived quantum memories based on spin waves, in the context of quantum repeaters and quantum networks

Coherent spin control at the quantum level in an ensemble-based optical memory

Long-lived quantum memories are essential components of a long-standing goal of remote distribution of entanglement in quantum networks. These can be realized by storing the quantum states of light as single-spin excitations in atomic ensembles. However, spin states are often subjected to different dephasing processes that limit the storage time, which in principle could be overcome using spin-echo techniques. Theoretical studies have suggested this to be challenging due to unavoidable spontaneous emission noise in ensemble-based quantum memories. Here we demonstrate spin-echo manipulation of a mean spin excitation of 1 in a large solid-state ensemble, generated through storage of a weak optical pulse. After a storage time of about 1 ms we optically read out the spin excitation with a high signal-to-noise ratio. Our results pave the way for long-duration optical quantum storage using spin-echo techniques for any ensemble-based memory.Comment: 5 pages, 2 figures, 1 tabl

Towards highly multimode optical quantum memory for quantum repeaters

Long-distance quantum communication through optical fibers is currently limited to a few hundreds of kilometres due to fiber losses. Quantum repeaters could extend this limit to continental distances. Most approaches to quantum repeaters require highly multimode quantum memories in order to reach high communication rates. The atomic frequency comb memory scheme can in principle achieve high temporal multimode storage, without sacrificing memory efficiency. However, previous demonstrations have been hampered by the difficulty of creating high-resolution atomic combs, which reduces the efficiency for multimode storage. In this article we present a comb preparation method that allows one to increase the multimode capacity for a fixed memory bandwidth. We apply the method to a $^{151}$Eu$^{3+}$-doped Y$_2$SiO$_5$ crystal, in which we demonstrate storage of 100 modes for 51 $\mu$s using the AFC echo scheme (a delay-line memory), and storage of 50 modes for 0.541 ms using the AFC spin-wave memory (an on-demand memory). We also briefly discuss the ultimate multimode limit imposed by the optical decoherence rate, for a fixed memory bandwidth.Comment: 10 pages, 8 figure

An analysis of the conditions for the implementation of policies of inclusive education in Brazil and in England

This paper analyses the conditions for the implementation of policies of inclusive education in Brazil and in the United Kingdom of England. These policies are inserted in a movement of exclusive characteristics that has affected the western societies since the Second World War. Opposing to this movement that excludes persons and groups from the world of work, consumption and social rights, inclusive policies affirm the necessity of providing education to all individuals in a society. The implementation of these policies, in both countries considered is regulated by laws and official documents that aim at specifying the educational actions to be taken by the educational systems. Inclusive practices, however, face barriers derived from the conflicts and tension generated by the general social conditions as well as from the properties of educational systems. These, generally, have not been designed to offer an education that meets different kinds of needs. The paper argues in favor of a better understanding of the conditions under which inclusive policies are implemented. The analysis of these conditions aims to contribute with the process of decision-making by educators, and to help them to establish the priorities and to choose the proper tools for educational practice.O artigo analisa as condições de implementação de políticas de educação inclusiva no Brasil e no Reino Unido. Essas políticas inserem-se em um movimento de características excludentes que tem afetado a sociedade ocidental desde o período posterior à Segunda Guerra Mundial. No sentido oposto ao desse movimento excludente, as políticas inclusivas afirmam a necessidade de garantir educação a todos os indivíduos de uma sociedade. A implementação dessas políticas, nos dois países considerados, é pontuada por um conjunto de leis e documentos oficiais que visa a especificar as ações inclusivas. As práticas, entretanto, esbarram tanto nos conflitos e tensões gerados pelas condições sociais gerais, como nas propriedades dos sistemas educacionais. O artigo argumenta em favor de uma melhor compreensão das condições de implementação das políticas inclusivas, de modo que o educador possa estabelecer, assim, as prioridades no seu contexto de atuação.68971