21090 research outputs found
Sort by
The complexity of constraint system games with entanglement
No full textConstraint satisfaction problems (CSPs) are a natural class of decision problems where one must decide whether there is an assignment to variables that satisfies a given formula. Schaefer's dichotomy theorem and its extension to all alphabets due to Bulatov and Zhuk, shows that CSP languages are either efficiently decidable or NP-complete. It is possible to extend CSP languages to quantum assignments using the formalism of nonlocal games. The recent MIP*=RE theorem of Ji, Natarajan, Vidick, Wright, and Yuen shows that the complexity class MIP* of multiprover proof systems with entangled provers contains all recursively enumerable languages. As a consequence, general succinctly presented CSPs are RE-complete. We show that a wide range of NP-complete CSPs become RE-complete when the players are allowed entanglement, including all boolean CSPs, such as 3SAT and 3-colouring. This implies that these CSP languages remain undecidable even when not succinctly presented.
Prior work of Grilo, Slofstra, and Yuen shows (via a technique called simulatable codes) that every language in MIP* has a perfect zero knowledge (PZK) MIP* protocol. The MIP*=RE theorem uses two-prover one-round proof systems. Hence, such systems are complete for MIP*. However, the construction in Grilo, Slofstra, and Yuen uses six provers, and there is no obvious way to get perfect zero knowledge with two provers via simulatable codes. This leads to a natural question: are there two-prover PZK-MIP* protocols for all of MIP*?
In this work, we show that every language in MIP* has a two-prover one-round PZK-MIP* protocol, answering the question in the affirmative. For the proof, we use a new method based on a key consequence of the MIP*=RE theorem, which is that every MIP* protocol can be turned into a family of boolean constraint system (BCS) nonlocal games. This makes it possible to work with MIP* protocols as boolean constraint systems. In particular, it allows us to use a variant of a CSP due to Dwork, Feige, Kilian, Naor, and Safra that gives a classical MIP protocol for 3SAT with perfect zero knowledge.
To prove our results, we develop a toolkit for analyzing the quantum soundness of reductions between constraint system (CS) games, which we expect to be useful more broadly. In this formalism, synchronous strategies for a nonlocal game correspond to tracial states on an algebra. We equip the algebra with a finitely supported weight that allows us to gauge the players' performance in the corresponding game using a weighted sum of squares. The soundness of our reductions hinges on guaranteeing that specific measurements for the players are close to commuting when their strategy performs well. To this end, we construct commutativity gadgets for all boolean CSPs and show that the commutativity gadget for graph 3-colouring due to Ji is sound against entangled provers. We define a broad class of CSPs that have simple commutativity gadgets. We show a variety of relations between the different ways of presenting CSPs as games. This toolkit also applies to commuting operator strategies, and our argument shows that every language with a commuting operator BCS protocol has a two prover PZK commuting operator protocol
Toward Decolonial Tourism Education in Ghana: A Critical Ethnography
No full text(English)
Tourism education, especially in institutions of higher learning has grown to become an important area in tourism literature since the 1980s (Fidgeon, 2010; Liburd, Hjalager, & Christensen, 2011; Sheldon, Fesenmaier, & Tribe, 2013). This development, especially in the Global South, has been largely due to the growth in the tourism industry, and the consequent need to develop a philosophical and pedagogical understanding into tourism. In Ghana, tourism education has remained deeply embedded in colonial frameworks, consequently influencing both pedagogical approaches and knowledge production. In this critical ethnographic study, I examine the relationship between tourism education and colonization in the Department of Hospitality and Tourism Management (DHTM) at the University of Cape Coast (UCC). Through this methodological approach, I unpacked how tourism education either reinforces and / or resists colonial knowledge structures while exploring decolonial alternatives that centre Ghanaian and African epistemologies. I drew on epistemic decolonization theories (Chambers & Buzinde, 2015; Grosfoguel, 2007) to challenge dominant Western and Eurocentric paradigms and to offer alternative possibilities of tourism educational practices that unsettle colonialist thought, organization, and infrastructure of current tourism education, trends, policies, and practices that have existed in the DHTM, UCC. Through in-depth interviews with faculty, students, and staff, as well as participant observations, I found that while some faculty members actively resist colonial dominance by incorporating Ghanaian and African perspectives into their teaching, structural barriers hinder the full decolonization of tourism education in the department. The study therefore highlights the importance of participatory curriculum development, storytelling, and oral histories as legitimate knowledge transmission methods, aligning with broader calls for decolonial pedagogical practices (Mbembe, 2016). Additionally, the study critiques the Eurocentric organization of knowledge in academic libraries and the marginalization of African-authored works. It advocates for a restructured classification system that prioritizes Ghanaian and African scholarship to foster epistemic decolonization. The research suggests that decolonizing tourism education requires more than superficial curriculum changes. Instead, structural transformation of knowledge production, educational infrastructure, and pedagogical approaches are required for any effective decolonial transformation to happen. This dissertation contributes to ongoing discussions on Africanization and decolonization in higher education, urging educators and policymakers to reimagine tourism education in a way that is responsive to local histories, cultures, and aspirations.
(Ewe)
Tsaɖiɖi ŋuti hehenana, vevietɔ le suku kɔkɔwo me va zu akpa vevi aɖe le tsaɖiɖi ŋuti agbalẽwo me tso ƒe 1980-awo me (Fidgeon, 2010; Liburd, Hjalager, & Christensen, 2011; Sheldon, Fesenmaier, & Tribe, 2013). Ŋgɔyiyi sia, vevietɔ le Xexeame Katã ƒe Anyiehe la, tso tsaɖiɖi ƒe dɔwɔƒewo ƒe dzidziɖedzi gbɔ koŋ, kple alesi wòhiã be woatu xexemenunya kple nufiafia gɔmesese ɖo ɖe tsaɖiɖi me tso esia ta. Le Ghana la, tsaɖiɖi ŋuti hehenana gakpɔtɔ ƒo ke ɖe to ɖe dutanyigbadziɖuɖu ƒe ɖoɖowo me vevie, si wɔe be ekpɔ ŋusẽ ɖe nufiafiamɔnu kple sidzedze wɔwɔ siaa dzi. Le ameƒomeviwo ŋuti numekuku vevi sia me la, medzro ƒomedodo si le tsaɖiɖi ŋuti hehenana kple dutanyigbadzinɔlawo dome le Department si woyana be Hospitality kple Tourism Management (DHTM) le Cape Coast Yunivɛsiti (UCC) me. To mɔnu sia dzi la, meɖe alesi tsaɖiɖi ŋuti hehenana doa ŋusẽ kple / alo tsi tre ɖe dutanyigbadzinɔlawo ƒe sidzedze ƒe ɖoɖowo ŋu esime mele dutanyigbadziɖuɖu ƒe mɔnu bubu siwo le titina na Ghana kple Afrika ƒe sidzedzeŋutinunyawo me dzrom. Me za epistemic decolonization nusɔsrɔwo (Chambers & Buzinde, 2015; Grosfoguel, 2007) tsɔ tsi tre ɖe Eurocentric paradigms siwo xɔ aƒe ɖe amewo me ŋu eye matsɔ tsaɖiɖi ƒe hehenana nuwɔna bubu siwo ate ŋu adzɔ siwo tɔtɔa dutanyigbadziɖuɖu ƒe susu siwo nɔ anyi le DHTM, UCC me la ana. To gbebiame deto siwo wowɔ kple nufialawo, sukuviwo, kple dɔwɔlawo, kpakple gomekpɔlawo ƒe ŋkuléleɖenuŋu me la, mekpɔe be togbɔ be nufialawo dometɔ aɖewo tsia tre ɖe dutanyigbadziɖuɖu ƒe ŋusẽkpɔɖeamedzi ŋu vevie to Ghanatɔwo kple Afrikatɔwo ƒe nukpɔsusuwo dede woƒe nufiafia me hã la, xɔtuɖoɖo ƒe mɔxenuwo xea mɔ na tsaɖiɖi ŋuti hehenana ƒe dutanyigbadziɖuɖu bliboe ɖeɖeɖa le dɔwɔƒea. Eyata numekukua te gbe ɖe gomekpɔkpɔ le nusɔsrɔ̃ɖoɖowo wɔwɔ, ŋutinya gbɔgblɔ, kple ŋutinya siwo wogblɔ kple nu ƒe vevienyenye dzi abe sidzedze ƒe kakamɔnu siwo le se nu ene, si wɔ ɖeka kple yɔyɔ siwo keke ta wu be woawɔ nufiafiamɔnu siwo me woɖea dutanyigbawo ɖa le (Mbembe, 2016). Tsɔ kpe ɖe eŋu la, numekukua ɖe ɖeklemi sidzedze ƒe ɖoɖowɔwɔ si wotu ɖe Europa dzi le agbalẽdzraɖoƒe siwo me wosrɔ̃a nu le kple agbalẽ siwo Afrikatɔwo ŋlɔ la ɖeɖe ɖe aga. Eʋlia hatsotsowo me toto ƒe ɖoɖo si wogbugbɔ trɔ asi le si tsɔa Ghana kple Afrika ƒe agbalẽnyalagãwo ɖoa nɔƒe gbãtɔ be woatsɔ ado sidzedze ƒe dutanyigbawo ɖeɖeɖa ɖe ŋgɔ. Numekukua ɖee fia be tsaɖiɖi ŋuti hehenana ɖeɖeɖa bia nu geɖe wu nusɔsrɔ̃ɖoɖowo ƒe tɔtrɔ gotagometɔwo ko. Ke boŋ, ehiã be woatrɔ asi le sidzedze wɔwɔ, sukudede ƒe xɔtuɖoɖowo, kple nufiafiamɔnu ŋu le ɖoɖo nu hafi tɔtrɔ ɖesiaɖe si awɔ dɔ nyuie le dutanyigbawo ɖeɖeɖa me nate ŋu adzɔ. Nusɔsrɔ̃ sia kpena ɖe numedzodzro siwo yia edzi le Afrikatɔwo ƒe tɔtrɔ kple dutanyigbawo ɖeɖeɖa ŋu le suku kɔkɔwo me ŋu, eye wòƒoe ɖe nufialawo kple ɖoɖowɔlawo nu be woagbugbɔ akpɔ tsaɖiɖi ŋuti hehenana le susu me le mɔ si awɔ ɖeka kple nutoa me ŋutinyawo, dekɔnuwo, kple didiwo nu
Exploration, Synthesis, and Characterization of Bioinspired Iron–Imide and Iron–Amide Clusters
No full textIron-sulfur clusters with high-spin irons play a crucial role in various biological processes. These clusters are found in enzymes such as ferredoxins, aconitase, and nitrogenase, where they function as redox cofactors or active sites for catalysis. One particularly significant transformation is the reduction of atmospheric dinitrogen to ammonia, which occurs at a complex iron-sulfur cluster with core composition [MFe7S9C] where M = Mo, V or Fe. Notably, this cluster features a μ6-carbide, whose function in the cluster remains unclear.
In synthetic iron-sulfur chemistry, Fe4S4 clusters have been extensively studied with various ligands and core compositions. To explore the effects of light 2p-element ligation, nitrogen anions in amide or imide motifs can be employed. Research in the Lee group has led to the synthesis of a series of iron-imide-sulfide clusters [Fe4(NtBu)nS4-nCl4]z (n = 1-4). This class of compounds extends from [Fe4S4] to [Fe4(NtBu)4] cores, with intermediate species in the series containing a mixture of imide and sulfide ligands.
The [Fe4(NtBu)4] core is synthesized via the reaction of FeCl3 with two equivalents of LiNHtBu, yielding [Fe4(NtBu)4Cl4]1–, Fe4(NtBu)4Cl3(NtBu) and FeCl2(NH2tBu)2 as the primary iron-containing products, with an approximate combined in-situ yield of 50% based on starting iron content. The [Fe4(NtBu)4Cl4]1– species can be isolated in 24% yield and undergoes both chemical oxidation and reduction to form [Fe4(NtBu)4Cl4] and [Fe4(NtBu)4Cl4]2–, respectively. The [Fe4(NtBu)4Cl4]z series has been characterized using a range of spectroscopic and structural techniques to elucidate its solid-state and solution phase properties.
LiNHtBu is synthesized via the lithiation of tBuNH2 with one equivalent of n-BuLi. Upon workup, this reaction affords white crystals which display an octameric ladder structure with eight molecules of LiNHtBu in the solid state. When excess tBuNH2 (ca. 1.1 equivalents) is used, a white colloidal solution forms, yielding an infinite polymeric ladder structure in the solid state. The cyclic ladder structure was determined to be the metastable polymorph and the infinite polymer ladder structure was determined to be the thermodynamic polymorph using DSC analysis and synthetic procedures. The cyclic ladder structure can be converted to the infinite polymer structure by heat or by addition of a donor ligand to catalyze the transformation
The [Fe4(NtBu)S3Cl4]2– cluster is synthesized via a controlled synthetic protocol involving the formation of an iron-amide dinuclear intermediate, Fe2(μ-NHtBu)2[N(SiMe3)2]2. This intermediate arises from the protonolysis reaction of Fe[N(SiMe3)2]2 with tBuNH2. Notably, this transformation is unusual, as analogous reactions with Fe[N(SiMe3)2]2 typically proceed with ligands that are more acidic than HN(SiMe3)2. To explore the scope of this reactivity, a series of amines with varying acidity, steric hindrance and nitrogen substitution patterns were examined. The products that can form from reactivity of Fe[N(SiMe3)2]2 with amines include a mononuclear amine adduct, di– and tri–substituted dinuclear complexes and homo– and heteroleptic trinuclear complexes. The type of complex formed depended on the stoichiometry of amine to Fe[N(SiMe3)2]2 and the acidity, nitrogen substitution and steric hindrance around the nitrogen.
Finally, the reduction of [Fe4(NtBu)S3(SPh)4]2– was attempted. Although reduction to the z = 3– cluster was achieved, the resulting product proved unstable in CD3CN, decomposing into a new species accompanied by thiolate release. Upon oxidation of the decomposition product, [Fe4(NtBu)S3(SPh)4]2– was regenerated, indicating that the Fe4(NtBu)S3 core likely remains intact. Further ligand tuning revealed that the use of p-methylbenzene thiolate allowed for the isolation of the reduced cluster; however, purification was hindered by its limited solubility. The synthesis of the oxidized, [Et4N][Fe4(NtBu)S3(SMes)4] cluster was achieved by oxidization of the z = 2– cluster by ferrocenium. Surprisingly, the oxidized cluster displayed a ground spin state of S = 3/2
Multiphase Competition and Quantum Moment Fragmentation in Dipolar-Octupolar Pyrochlore Materials
No full textIn the field frustrated magnetism, magnetic pyrochlore oxides are one of the most widely explored platforms for realizing exotic phenomena in three dimensions, including classical, fragmented and quantum spin liquids.
In this thesis, we elaborate on the existing understanding of the low-temperature properties of a subclass of magnetic pyrochlore oxides -- the so-called dipolar-octupolar (DO) pyrochlores -- using various analytical and numerical techniques.
To begin, we explore the `XZ' line of the DO phase diagram, which exhibits a strong competition between neighbouring quantum spin liquid and long-range ordered phases using large-scale quantum Monte Carlo (QMC).
In particular, we examine how this competition can explain the low-temperature behaviours observed in moment fragmentation candidate Nd_2Zr_2O_7.
We proceed by examining the thermodynamics and correlations exhibited by another DO pyrochlore Ce_2Sn_2O_7, arguing that it too harbours moment fragmentation in the T=0 ordered state by comparing and contrasting its behaviour with Nd_2Zr_2O_7.
To further elaborate the extent of this phenomenon, we scan the XZ line discussing the evolution of fragmentation as one varies the microscopic exchange parameters between neighbouring ordered and disordered phases in the DO phase diagram.
Extending beyond the nearest-neighbour (NN) model, we present a derivation of the symmetry-allowed exchange interactions for the DO model up to third nearest-neighbours.
Taking a subset of these new exchange parameters, we construct a mean-field phase diagram centered at the NN exchange parameters presented for quantum spin ice candidate Ce_2Zr_2O_7.
In particular, we identify the ordering wavevectors characterizing the long-range order stabilized by lifting the degeneracy exhibited by the NNx model.
Further, we present estimates of the critical temperatures associated with the ordering transitions presented, defending the lack of order observed in experiments
Boredom and the Sense of Agency
No full textPrevious research has established boredom as an uncomfortable affective experience with a number of cognitive, physiological and behavioural correlates that are more prevalent for those who experience the state more frequently and intensely—the so-called boredom prone. The conundrum of boredom is that the individual fails to engage meaningfully with their environment despite the strong desire to do so. A proposed contributor to the experience of boredom that has had relatively little focus to date, is the sense of agency, the feeling of being an active contributor to one’s outcomes. This thesis explores the notion that agency is critical to the experience of boredom and boredom proneness. In Chapter 2 of this thesis, where boredom is conceptualized within a self-regulatory framework, the sense of agency negatively predicted boredom proneness in two separate samples (N= 283; N=1,358) over and above other known correlates of boredom proneness. In Chapter 3, the possibility that this relation was due to an impoverished capacity to perceive agency external to the self was explored. Results indicated that trait boredom showed no association with the perception of agency external to the self. In contrast, state boredom was negatively associated with perceptual judgements of agency, a relationship that was partially mediated by attentional engagement. Chapter 4 investigated the possibility that the highly boredom prone report a diminished sense of agency because they are less tolerant of disruptions to agency. Both state and trait boredom were significantly associated with metrics in this study indicative of an intolerance to agency disruption. Those high in boredom proneness tended to reset game play more frequently when faced with disruptions to agency and did so earlier than did those low in boredom proneness. This is taken to reflect a lower level of tolerance for disruptions to agency. Finally, Chapter 5 assessed possible cross-cultural influences of the association between boredom and agency given differences in the adherence to individualist and collectivist ideals. Culture showed only a minimal influence on the relation between boredom and agency, indicating that this relation is robust across multiple cultures. These results give meaningful insights into the individual differences that drive boredom proneness and emphasize that a strong sense of agency is imperative in responding to boredom’s signal to re-orient and engage more meaningfully
Learning to Concurrently Execute Multiple Robotic Tasks – Analysis and Optimization-Based Synthesis
No full textIn this thesis, we develop and analyze a general framework for learning and concurrently executing multiple robotic control tasks learned within the paradigm of reinforcement learning – each encoded as a value function and executed together as constraints in a pointwise min-norm controller. Applying reinforcement learning to robotic control tasks is an active area of research as it has the potential to generalize to complex tasks. For robots that are redundant – meaning they have the physical capability of executing multiple tasks at the same time – it can be useful to learn to concurrently execute multiple control objectives. Previous and relatively recent work proposes a model-based approach of concurrently executing multiple tasks learned using reinforcent learning by incorporating the learned value functions as constraints in a pointwise min-norm controller. This work, however, does not enforce nor encourage any constraints on the learned value functions themselves, causing there to be no guarantees on how trained tasks execute together. Building on this approach, this thesis proposes ideas for enabling learned value functions to be concurrently executable when combined using the proposed pointwise min-norm controller. Firstly, we define notions of independence, orthogonality, concurrent executability and concurrent controllability to describe the relationships between value functions and their ability to execute together concurrently, based on the Lie derivatives of each value function. We then propose the idea of an “interference cost” which we prove can be used to train a set of value functions to be independent – meaning that their Lie derivatives are linearly independent, making it possible to pick inputs which concurrently execute each task. This interference cost can be used with any reinforcement learning algorithm, but we also propose a variant of fitted value iteration which can be used to efficiently learn such value functions. Additionally, we propose theory that provides necessary and sufficient conditions for value functions to be concurrently executable, using the proposed pointwise min-norm controller, within subsets of the state space. Finally, we test our proposed methods and theorems on simulations involving teams of mobile robots
Kraft Lignin as a Sustainable Flame Retardant Additive for Polymer Composites
No full textPlastic waste is a widespread and continuing issue, including the leaching of toxic additives from microplastics. Lignin is the second most abundant biopolymer, and although previously considered as waste and used as fuel, lignin’s availability and unique properties have garnered popularity as a sustainable and functional additive in many material applications. In this thesis, the versatility of lignin is explored at varying levels of valorization.
The first part of this work explored three differing purities of lignin and their effect on the properties of polyvinyl chloride (PVC) composites. These were tested alongside composites with differing concentrations of lignin and were all subject to various thermomechanical and flammability testing. Additionally, the decomposition kinetics of PVC and a lignin-PVC composite were explored. The industrially purified lignin outperformed the other purities mainly in mechanical properties, but the laboratory purified lignin retained the most heat capacity compared to the control. Additionally, at a concentration of 18 wt.% lignin, combustion indices were improved by 50 to 80%, but the elongation at break of these composites were reduced by 38.7%.
The second part of this work focused on incorporating a hydrophilic FR (ammonium polyphosphate) into natural rubber (NR), a hydrophobic polymer, by utilizing nano-containers constructed via the crosslinking of lignin. The properties of the lignin nanocontainers (LNCs) were studied to best enhance the dispersion of this filler within the NR at varying concentrations. These composites were tested alongside bulk incorporated lignin & FR as well as foamed samples to best determine the value brought by the LNCs. At a concentration of just 10 wt.% LNC, various flammability parameters improved and outperformed the bulk incorporated sample. This work demonstrated the versatility of lignin to by adding value to polymeric materials without additional modification or being modified to improve its incorporation as a nanomaterial
Cued by music: Eliciting autobiographical memories across the lifespan and assessing their emotionality
No full textMusic holds a unique capacity to involuntarily and rapidly evoke autobiographical memories (AMs), yet the source of its cueing ability is unspecified. In experiment 1, I examined what components of music are most beneficial in triggering AMs. Younger adults were presented with short clips of popular songs from their youth as memory cues, that were either unmodified, instrumental versions, lyrics-only, or a visual presentation of song and artist name. If participants experienced a memory, they provided a description of it. Unmodified song clips were most effective at evoking memories, and recall was enhanced in those high in trait music-related reward sensitivity. I also found evidence of temporal alignment between the song’s year of popularity, and timeframe of the evoked AMs. Given the powerful cueing effect of music on AMs, in experiment 2 I examined whether the findings would generalize to an older adult population, and whether music could serve to reduce age-related episodic memory deficits. Strikingly, song cues evoked more AMs in older than younger adults, offering a means of enhancing access to personal memories. I observed a temporal alignment between the year of popularity of the song cue and the time frame of the evoked memory in both age groups. I propose that songs are particularly effective memory cues because they help set temporal context, constraining the search for AMs to a specific point in time, facilitating access. These findings are particularly relevant for older adults who may have difficulty spontaneously recreating context. In chapter 3, I investigated whether computational approaches using natural language processing can be employed to examine emotional sentiment within autobiographical narratives. Current methods of analysis require extensive manual human coding, limiting the sample size that can feasibly be examined. I compared the congruence in classification of two popular lexicon-based sentiment analysis tools, VADER and TextBlob, with self-reported valence of 3,309 AM narratives from two datasets. Confusion matrices showed better congruence using VADER than TextBlob. Accuracy improved significantly when classification required binning valence into three rather than five categories, regardless of dataset size. Results suggest sentiment analysis is a promising avenue to determine broad classifications of valence within AM narratives. Overall, this thesis shows that songs are powerful cues for eliciting personal memories and can reduce age-related memory decline by setting the temporal context, facilitating access to content. Moreover, this thesis shows that VADER is a sentiment analysis approach that can be reasonably used to determine emotional valence, offering a means of characterizing autobiographical memory narratives
Planar Microcavity-enhanced Lasing from Semiconducting Carbon Nanotubes
No full textSingle-walled carbon nanotubes (SWCNTs) exhibit exceptional optical properties, including strong oscillator strength, size- and chirality-dependent tunable bandgap energies, and near-infrared (NIR) photoluminescence (PL) at room temperature. These features make them highly attractive and promising candidates for a wide range of optoelectronic and quantum optical applications. However, their practical deployment has been significantly hindered by several challenges such as PL quenching due to nanotube bundling, structural degradation from high-temperature annealing, or internal loss mechanism of exciton-exciton annihilation (EEA) under high excitation power. To overcome these challenges and enhance the radiative efficiency of SWCNTs, we design and fabricate wafer-scale dielectric distributed Bragg reflectors (DBR) to construct high-quality Fabry-Perot (FP) planar microcavities, where thin films of chirality-sorted, well-dispersed SWCNTs. These cavities serve to promote strong light-matter coupling between confined cavity photons and excitons in the SWCNT films. We perform optical characterization of the SWCNT-embedded microcavity devices both in weak and strong light-matter coupling regimes. First, in the strong coupling regime, we observe the SWCNT exciton-polariton dispersions with vacuum Rabi splitting (VRS) strength around 210 meV. Unfortunately, the polariton condensation was not achieved, primarily due to internal material loss mechanisms such as EEA process or strong reabsorption. On the other hand, we observe nonlinear lasing behavior in weak light-matter coupling regime, evidenced by a pronounced spectral linewidth narrowing signature with increasing excitation power. This would represent the first demonstration of lasing from SWCNT thin films integrated into planar dielectric microcavities, marking a significant milestone in carbon-based nanophotonics. While the results are promising, there remains considerable scope for enhancing the coherence and quality of the emitting light from these SWCNT-embedded microcavity devices, an essential step toward realizing scalable quantum nanophotonic platforms
Anonymous Communication within Highly Repressive Regions
No full textRepressive governments are increasingly resorting to restricting the flow of information during times of political unrest or civil resistance. In recent years, this restriction has taken new forms, expanding beyond traditional censorship tactics such as IP and DNS blocking to the use of Intranets (internal networks) and complete internet blackouts. To address this, many tools have been proposed to support users during such bleak times. However, most of these tools either overlook the importance of user anonymity or underestimate the lengths to which a censor might go to de-anonymize users.
In this thesis, we propose two new tools to help users reclaim their freedom and privacy under these restrictive conditions. First, we present Anix, an anonymous, blackout-resistant microblogging app that supports message endorsing, allowing users to avoid falling victim to misinformation, even without internet access. Second, we introduce Huma, a censorship circumvention tool that operates via web protocol tunneling and leverages deferred traffic replacement to counter a wide range of adversarial attacks. Additionally, Huma can function as a blocking-resistant anonymous communication system within Intranets. Together, these tools offer secure and private solutions for users facing the aforementioned restrictive scenarios. We implement and evaluate both tools to demonstrate their practicality and release our code as an open-source contribution to the community