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Coherent: Benefiting From Migration To Ethernet Switching Attached To AI/ML…

Coherent: Benefiting From Migration To Ethernet Switching Attached To AI/ML…

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    Enhanced Efficiency of GaAs Single-Junction Solar Cells with Inverted-Cone-Shaped Nanoholes Fabricated Using Anodic Aluminum Oxide Masks

    The GaAs solar cells are grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) and fabricated by photolithography, metal evaporation, annealing, and wet chemical etch processes. Anodized aluminum oxide (AAO) masks are prepared from an aluminum foil by a two-step anodization method. Inductively coupled plasma dry etching is used to etch and define the nanoarray structures on top of an InGaP window layer of the GaAs solar cells. The inverted-cone-shaped nanoholes with a surface diameter of about 50 nm are formed on the top surface of the solar cells after the AAO mask removal. Photovoltaic and optical characteristics of the GaAs solar cells with and without the nanohole arrays are investigated. The reflectance of the AAO nanopatterned samples is lower than that of the planar GaAs solar cell in the measured range. The short-circuit current density increased up to 11.63% and the conversion efficiency improved from 10.53 to 11.57% under 1-sun AM 1.5 G conditions by using the nanohole arrays. Dependence of the efficiency enhancement on the etching depth of the nanohole arrays is also investigated. These results show that the nanohole arrays fabricated with an AAO technique may be employed to improve the light absorption and, in turn, the conversion efficiency of the GaAs solar cell.

    Introduction

    GaAs is commonly used to fabricate the high conversion efficiency III-V solar cell based on multijunction tandem structure. An InGaP layer is utilized as a window layer on top of the GaAs emitter in a GaAs-based solar cell. Because of refractive index difference between InGaP and air, more than 30% of the incident light can be reflected from the surface of the solar cells [1]. It is therefore necessary to use an antireflection coating layer for improving the conversion efficiency. An antireflection coating using multilayers with different refractive index materials such as MgF2, ZnS, ZnO, SiO2,

    is usually used for the conventional solar cells [2–4]. However, this layer can invoke unexpected problems such as adhesion and thermal mismatch when the solar cell operates under the strong-irradiation condition. To overcome these drawbacks, surface texturing techniques have been successfully introduced [1, 5–7]. By patterning the window surface layer, one can significantly reduce the reflection of the incident light through the enhanced absorption from the textured structures. Nanopatterning structures using metal nanoparticles or photonic crystal have attracted much attention because they can improve the light absorption due to the plasmonic and spontaneous effects [8, 9]. Several groups reported on using two-dimensional photonic crystals to improve conversion efficiency of Si or Ge solar cells [10, 11]. However, using expensive nanopatterning technique such as electron-beam lithography increases device cost significantly. Therefore, nonlithographic approach using nanoporous anodic aluminum oxide (AAO) template has attracted a lot of attention as a key nanofabrication method due to its simple and low-cost process [12]. over, with the AAO mask, we can fabricate the nanohole arrays with a small diameter (below 100 nm) that is difficult to make by the conventional lithography methods. It is worth noting that by using such a small opening mask, we can fabricate the nanoholes with an inverted cone shape that is close to the optimized form for the light-management architectures to achieve the high-efficiency solar cells [13].

    In this study, we report on the improvement of the GaAs solar cells with the nanohole arrays on the InGaP window layer. The AAO masks with an opening size of about 50 nm are prepared using a two-step anodization process. The inverted-cone-shaped (ICS) nanoholes with different depths are formed on the surface of the solar cell after inductively coupled-plasma reactive-ion-etching (ICP-RIE) processes. The conversion efficiency improved from 10.53 to 11.57% under 1-sun AM 1.5 G conditions by using the nanohole arrays.

    Experiment Details

    The GaAs single-junction solar cell structures, as shown in Figure 1, are grown in a metalorganic chemical vapor deposition (MOCVD) system on n-type GaAs (100) substrates. Trimethylgallium (TMGa) and trimethylindium (TMIn) are used as group III precursors, while arsine (AsH3) and phosphine (PH3) are used as As and P sources, respectively. Silane (SiH4) and diethylzinc (DEZn) are used as n- and p-doping sources, respectively. Ultra-high purity hydrogen gas (H2) is used as a carrier gas. The reactor pressure and temperature are kept at 50 mbar and 680°C, respectively. Device structures from the substrate to the top consist of a 0.2 μm thick GaAs buffer layer for high crystal quality, a 0.05 μm thick highly doped In0.5Ga0.5P back surface field (BSF) layer, a 3.5 μm thick GaAs base layer, a 0.5 μm thick GaAs emitter layer, a 0.2 μm thick highly doped In0.5Ga0.5P window layer, and a 0.3 μm thick GaAs cap layer for ohmic contact.

    The solar cell devices with the aperture area of 0.25 cm 2 are made using conventional fabrication processes. Metal contacts are defined by a UV photolithography technique. AuGe/Ni/Au and Ti/Pt/Au layers are deposited by an e-beam evaporator for the n- and p-type ohmic contacts, respectively. The samples then are annealed in an RTA station at 385°C for 30 s. The InGaP window layer is exposed by selectively etching p GaAs cap layer in an acid solution (CA : H2O2 : H2O = 25 : 1 : 75).

    Nanohole arrays are patterned on the surface of the solar cell by an ICP-RIE etching using the AAO mask. The AAO masks are prepared by a typical two-step anodization process using a grain-free aluminum foil (99.99%, 100 μm in thickness, Tokai). The aluminum foil is electropolished in a 1 : 4 solution of perchloric acid and ethanol. After the first anodization in the 0.3 M oxalic acid at 40 V for 8 h, the anodized oxide layer on the Al foil is removed in a mixture of H3PO4 and CrO3. The sample is then exposed for the second anodization step resulting in a thin alumina film of 500–600 nm on top of the Al foil by controlling the anodization duration. A saturated HgCl2 solution is used to remove the Al film at the bottom, leaving a thick anodized alumina layer. The removal of the barrier layer and hole widening are conducted in a 5 wt % H3PO4 solution. The AAO masks are designed with a hole size of about 40 nm and a distance between holes of about 100 nm in a quasihexagonal geometry [14]. The AAO mask is placed on top of the GaAs solar cell structure. ICP-RIE etching is then applied to transfer the nanopattern from the AAO mask to the window layer of the solar cell. The etching process uses a mixture of BCl3 and Cl2 with the flows of 5 and 30 sccm, respectively, under an ICP source power of 200 W and an RF bias power of 50 W at a chamber pressure of 10 mTorr. The depths of the nanohole arrays are controlled by etching time that is varied from 10 to 60 s. The nanohole arrays are finally formed on top of the GaAs solar cell after removing the AAO masks. A GaAs solar cell without the nanohole pattern is used as a reference for the solar cell performance investigation. The morphologies of the GaAs solar cell with the nanohole arrays are studied by a field emission scanning electron microscopy (FE-SEM). To study the loss of the incident light, we carried out reflectance measurements at room temperature with a UV-Vis-NIR Cary 5000 Spectrometer from 300 to 900 nm. The photovoltaic current density-voltage (J-V) characteristics of the GaAs solar cells are evaluated by a solar simulator under 1-sun air mass (AM) 1.5 G-conditions at room temperature. The photocurrent response of the fabricated cells is also investigated with a quantum efficiency measurement system at room temperature.

    Results and Discussions

    Figure 2 shows the SEM images of the nanohole arrays on the solar cells. After a 40 s ICP/RIE etching and removal of the AAO mask, the nanohole arrays have the quasihexagonal symmetry with a mean diameter and depth of about 50 and 64 nm, respectively. The holes that formed on top of the solar cells are slightly larger than those of the AAO masks because the AAO masks may be etched out during the plasma etching process and/or the surfaces of solar cells in contact with the AAO masks are not completely smooth [12]. It is worth to note that the nanohole arrays retain an ICS form as can be observed clearly in the inset of Figure 2(b). The ICS nanoholes can be formed after a short-time dry etching process using masks with a small opening [15]. The depths of the nanohole arrays are measured to be about 16, 48, 64, and 95 nm for 10, 30, 40, and 60 s etching times, respectively.

    (a)

    (b)

    (a) (b)

    Datacom Optical Modules and Coherent

    While 400G Ethernet optical transceivers are used predominantly in hyperscale data centers, and many enterprise businesses are currently operating on 40G or 100G, data center connectivity development already is moving toward 800G.

    Datacom optical modules, also known as data communication optical modules, are transceiver devices used in data communication networks to transmit and receive data over optical fiber cables. These modules convert electrical signals into optical signals and vice versa, enabling high-speed and long-distance data transmission.

    At the cutting edge of datacom technology, the latest development is the emergence of 800G optical modules. These modules offer significantly higher data rates and bandwidth compared to previous generations, allowing for faster and more efficient data transmission in data centers and high-performance computing environments.

    Coherent ( NYSE:COHR ): Finisar, now a part of Coherent (acquired by II-VI in 2019), is a renowned supplier of optical communication modules. They offer advanced optical modules, including 800G solutions, designed for high-speed data transmission. The module features 16 channels of 50G NRZ transmitters and receivers in a 15 mm x 15 mm x 4 mm multimode CPO 800G VCSEL-based engine. The entire analog front end, including the driver, VCSEL, photodiode, and transimpedance amplifier, consumes less than 4 pJ/bit. Each VCSEL is paired with another unpowered device to enable 100% cold sparing for extremely high reliability.

    Although 70% of the world’s top 10 manufacturers of optical modules are from China in 2022, the localization rate of optical chips above 25G is only 5%, and high-end optical chips are still in the hands of U.S. manufacturers such as Coherent and Cisco. Coherent, through Finisar, has been the leading manufacturer of these transceivers for the past 22 years, as shown in Table 1.

    Driving Forces for Coherent in Artificial Intelligence and Primer

    Coherent will benefit from AI when Ethernet is more widely deployed.

    Ethernet is Growing Compared to InfiniBand Networking Protocols

    Ethernet and InfiniBand are two leading networking protocols. While Ethernet has made significant progress in terms of speed and features, and its adoption has expanded in data center environments, it doesn’t necessarily mean that InfiniBand will be completely replaced in the near future.

    With bandwidth in AI growing, the portion of Ethernet switching attached to AI/ML and accelerated computing will move from a niche today to a significant portion of the market in 2027, according to 650 Group. By 2027, nearly one in five Ethernet Switch ports sold into the data center will be related to AI/ML and accelerated computing.

    • Ethernet comprises over 25% of AI/ML Networking in 4Q 2022.
    • The AI Networking market (including switch silicon) will grow to 10 billion in 2027 from 2 billion in 2022 at nearly 40% CAGR.
    • Ethernet will grow to 6 billion from 0.5 billion.
    • InfiniBand will grow to 4 billion from 1.5 billion.
    coherent, benefiting, migration, ethernet, switching

    In the context of networking, an AI/ML switch refers to a network switch that incorporates artificial intelligence (AI) and machine learning (ML) capabilities to enhance its functionality and performance.

    Chart 1 shows a slide with a different analysis from a Cisco live presentation that the AI/ML TAM (total available market) will grow at a CAGR of 42%, growing from 2.1 billion in 2023 to 8.5 billion in 2027. In this analysis, Ethernet will grow from 25% to 75% in 2027, even higher than the 60% share by the 650 Group analysis. This growth will be an opportunity for Coherent.

    The higher-speed segments of the Ethernet switch market continue to see strong growth according to IDC, driven by hyperscalers and Cloud providers building out datacenter network capacity. Market revenues for 200/400 GbE switches rose more than 300% for the full year in 2022 and rose 141.3% annually in 1Q23 to 10 billion and up 14.3% QoQ. 100GbE revenues increased 18.2% year over year in 1Q23. 25/50 GbE revenues increased 21.1% in 1Q23.

    Continued Improvements in Coherent Transceivers

    Cloud and artificial intelligence (AI) service providers are ramping up deployments of 400G and 800G transceivers for their megascale data-center buildouts, with an eye on 1.6T transceivers in the future. Coherent is introducing high-power CW DFB laser diodes that enable 400G to 1.6T silicon photonics-based transceivers, which are among the transceiver technology platforms deployed in the data-center mid-reach range of 500m to 2km.

    The transceivers come in a OSFP form factor with 200G PAM4 per lane optical and 100G PAM4 per lane electrical interfaces, with an optical reach of up to 2 km. This transceiver is for use in the next generation of 25T and 50T Ethernet switches. It represents a natural evolution from transceivers with 100G optical lanes and is more power-efficient and cost-effective than previous generations. This technology is expected to form the core of the second generation of 800G transceivers and the first generation of 1.6T transceivers. They represent a natural evolution from transceivers with 100G optical lanes and are more power-efficient and cost-effective. Initial applications are anticipated in hyperscale datacenters, with enterprise applications to follow.

    Investor Takeaway

    The fact that Coherent, through Finisar, has been the market leader of these transceivers for the past for the past 22 years is telling.

    Chart 2 shows share price performance for Coherent. As I noted in my June 2, 2023, Seeking Alpha article entitled “Coherent: Short-Term Macro Headwinds Have Been Outweighing Silicon Carbide Tailwinds,” Coherent has been impacted by exposure to macro factors coming from consumer and communication downturns.

    In Chart 2, I also show share price performance for C3.ai (AI) and GSI Technology (GSIT), which are significant players in the AI space. All three companies have been impacted by investor pull backs in AI. In the past five days, COHR share performance is.21.1%, AI is.27.2%.

    Coherent is more than an AI company. But if one looks at Coherent’s FOCUS in 2023, nearly every product press release is on lasers. In fact, 14 press releases in 2023 addressed new laser technology and two on optical communications. So it’s apparent Coherent management is moving in that direction.

    coherent, benefiting, migration, ethernet, switching

    This free article presents my analysis of this semiconductor sector. A more detailed analysis is available on my Marketplace newsletter site Semiconductor Deep Dive. You can learn more about it here.

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    Three-junction III-V solar cell with 29.3% efficiency

    Japanese researchers have built an InGap-GaAs-CIGS solar cell that purportedly has the potential to reach an efficiency of 35%. The device has already achieved an efficiency of 31.0%, an open-circuit voltage of 2.97 V, a short-circuit current density of 12.41 mA/cm2, and a fill factor of 0.80.

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    Researchers led by Japan’s National Institute of Advanced Industrial Science and Technology (AIST) have fabricated a three-junction solar cell based on indium gallium phosphide (InGaP), gallium arsenide (GaAS) and copper, indium, gallium and selenium (CIGS) with a mechanical stacked design.

    “We are currently increasing our efforts to improve the cell efficiency and the development of the mass production technology,” researcher Kikuo Makita told pv magazine, noting that this kind of cell has the potential to achieve efficiencies close to 35%.

    The scientists built the cell with a two-junction InGap-GaAs upper cell with a bandgap of 1.49 eV, based on a rear-emitter heterojunction structure developed by Japanese manufacturer Sharp, and a CIGS bottom device with a bandgap of 1.01 eV. with improved surface roughness. They connected the cells through a modified Smart stack with palladium (Pd) nanoparticles and adhesive.

    The research group improved the bottom cell’s surface via wet etching. They used a bromine-based solution and modified its thin transparent conducting oxide (TCO) layer.

    “Surface roughness leads to an increase in the gap width at the bonding interface,” they explained, noting that this roughness, combined with the TCO thickness may lead to reflection loss. “Therefore, in this study, we focused on minimizing surface roughness and TCO thickness.”

    The academics tested the performance of the cell under standard illumination conditions. They found it achieved a power conversion efficiency of 29.3 % for the aperture area (31.0% for the active area), an open-circuit voltage of 2.97 V, a short-circuit current density of 12.41 mA/cm 2. and a fill factor of 0.80.

    They said the obtained efficiency of 29.3% is superior to that of the group’s previous results. They claimed it was the highest value ever reported for any two-terminal GaAs.CIGSe-based multijunction solar cell.

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    “We examined the costs of the cells using Smart stack technology and, according to our simulation, they may result in a final module cost of US 2/W,” Makita said. “GaAs cell cost, CIGSe cell cost, bonding cost, and modulization cost are 86%, 7%, 3%, and 4%, respectively.

    The GaAs cell, especially the GaAs substrate and GaAs epi-growth, is the main factor affecting device-fabrication costs.

    “In our project, device epitaxial lift-off (ELO) and substrate reuse techniques are studied to reduce the GaAs substrates costs,” Makite said. “In addition, the AIST has developed a hydride vapor phase epitaxy (H-VPE), which is a new growth method for GaAs cells. H-VPE is a low-cost technique compared to the general metal-organic chemical vapor deposition (MOCVD) technique. We think that the development of these fabrication technologies contributes to the cost reduction of expensive GaAs cells.”

    The researchers presented the cell design in “Mechanical stacked GaAs//CuIn1−yGaySe2 three-junction solar cells with 30% efficiency via an improved bonding interface and area current-matching technique,” which was recently published in Progress in Photovoltaics. The cost of producing solar cells based on compounds of III-V element materials – named according to the groups of the periodic table that they belong to – has confined such devices to niche applications, including drones and satellites, where low weight and high efficiency are more pressing concerns than costs in relation to the energy produced.

    Fraunhofer ISE researchers recently achieved a 35.9% conversion efficiency for a III-V monolithic triple-junction solar cell based on silicon. In August 2020, the research institute announced a 25.9% conversion efficiency rate for a III-V tandem solar cell grown directly on silicon. This cell is a modified version of a 34.5%-efficient III-V solar cell that is manufactured through a process known as direct wafer bonding, where the III-V layers are first deposited on an aluminum gallium arsenide (GaAs) substrate and then pressed together.

    Researchers at Tampere University in Finland recently developed a III-V multi-junction solar cell that purportedly has the potential to reach a power conversion efficiency of close to 50%. The National Renewable Energy Laboratory (NREL) in the United States announced a 32.9% efficiency for a tandem cell device utilizing III-V materials last year.

    This content is protected by copyright and may not be reused. If you want to cooperate with us and would like to reuse some of our content, please contact: editors@pv-magazine.com.

    Emiliano Bellini

    Emiliano joined pv magazine in March 2017. He has been reporting on solar and renewable energy since 2009.

    Types of Solar Panels

    All solar panels are not the same. They differ in performance, appearance, price, material, application, and size. The types of solar panels you need for your home or office depends on the roof size, consumption, budget, efficiency, among other factors.

    There are 3 common kinds of solar panels:

    • Monocrystalline solar panels
    • Polycrystalline solar panels
    • Thin-film solar panels

    Although there are other types of solar panels, most are not economically or technologically viable.

    The types of solar panels are classified into 3 groups. The classification is based on the kind of materials used and the commercialization of the product.

    • First-generation solar panels
    • Second-generation solar panels
    • Third-generation solar panels

    First Generation Solar Panels

    Monocrystalline and polycrystalline solar panels fall under this category. The cells are made of crystalline silicon and gallium arsenide (GaAs) wafers. They are the most common types of solar panels in commercial and residential solar panel installation. Because of their widespread use, they are also referred to as conventional or traditional solar panels.

    First-generation solar panels are the oldest PV cells, and their fabrication and technological applications are well-known. GaAs is a better material than silicon because it has higher optical properties. Therefore, it requires thicker silicon wafers to harness the same amount of energy as GaAs.

    But, gallium and arsenide are expensive and not commercially viable for the manufacture of solar panels. The materials are limited on the surface of the earth. Therefore, silicon remains the primary material in the manufacture of solar panels.

    Let’s have a look at each of the solar panel types under the first generation.

    Monocrystalline Solar Panels

    The solar cells are made of the purest form of silicon. They have a uniform silicon composition, which gives them high efficiency. They have rounded edges because silicon crystals are cylindrical. You can identify the panels from the even rows and columns.

    The silicon wafers used in monocrystalline cells have high efficiency (up to 20%) compared to other types of solar panels. Therefore, you require fewer monocrystalline solar panels; this makes them ideal for use in small-sized roofs. You can also use this type in pole mounts because the space is also limited.

    However, the price of monocrystalline solar panels is higher. They are more costly to manufacture than the other types. The solar panels have a longer lifespan because of increased resistance to temperatures; thus, a more extended warranty. The monocrystalline solar panel system could last for more than 30 years.

    Polycrystalline Solar Panels

    Do you want to install cheap solar panels, and you have unlimited roof space? Polycrystalline solar cells have lower efficiency but are feasible for residential buildings where space may not be a problem. The panels are also referred to as multi-crystalline solar panels.

    Although they are made from the same material as monocrystalline, they have lower efficiency, ranging between 15-17%. The solar panels have a speckled bluish color, which many homeowners consider unattractive. Another difference from the former type is the appearance. Polycrystalline solar panels have sharp wafer edges because of how they are manufactured.

    A decade ago, polycrystalline solar panels were the most common type of solar panels. However, their popularity has dwindled because of low efficiency. The average capacity of an average polycrystalline solar panel system is approximately 300 watts. Therefore, you require around 20 for a 6 kW solar panel system.

    The life expectancy of polycrystalline solar panels is lower. Thus, a shorter warranty period than monocrystalline solar panels. The choice between polycrystalline and monocrystalline solar panels is not outright. Each has its ideal application, depending on your situation. You should go for multi-crystalline solar panels if you want to cut on cost and the size of your roof or ground mounts is not limited. However, the panels are affected by high temperatures, which can lower their lifespan.

    Second Generation Solar Panels

    Thin-film solar panels make up the second generation of solar panels. some of the most common types of 2 nd generation solar cells include:

    • Amorphous silicon solar panels
    • Cadmium telluride (CdTe)
    • Copper indium gallium selenide (CIGS)
    • Concentrated photovoltaic cells (CVP)

    Thin-film solar panels have lower efficiency than the crystalline types because of the material used. They are common in utility-scale applications where space is plenty.

    Amorphous Silicon

    Amorphous silicon (a-Si) solar panels are made of hydrogenated silicon, which has low energy conversion efficiency. The material is deposited in flexible substrates like metal, plastic, and glass. The solar panels are less durable compared to crystalline silicon cells; thus, a shorter warranty period.

    Cadmium telluride

    CdTe solar panels are made from semi-conductors pressed between thin films of glass. There are concerns about cadmium safety, but studies show that a compound of the two elements has lower toxicity than Cd alone. Therefore, proper disposal of the material is advisable to prevent any adverse health effects. This type of solar panel is the most common in commercial thin-film applications.

    Copper indium gallium selenide

    CIGS solar panels are an exciting option because of their high efficiency. However, the cost of manufacturing solar cells makes them an expensive option. It is difficult for copper indium gallium selenide solar panels to compete with crystalline silicon cells. However, the solar panels have a higher efficiency than other kinds.

    Thin-film solar panels are the most flexible. They can adopt different shapes for aesthetic value. There are many studies to improve solar panels’ efficiency and overcome the commercial and technological barriers of the solar cells.

    Concentrated photovoltaic cells

    CPV is a new technology that uses curved mirrors and lenses to concentrate sunlight to highly efficient solar cells. The solar panels can achieve an efficiency of up to 41%, which is double what the second most efficient type can harness. The technology’s commercial application will be a significant breakthrough in solar energy because it will reduce the cost and space required to install solar panels.

    Third Generation Solar Panels

    There is a limit to the efficiency of solar panels. Shockley-Queisser ranges between 31-41% for a single bandgap solar cell. The third-generation of solar panels seeks to overcome this limit and improve efficiency. The main objective of the technology is to convert solar cell non-compatible light frequencies to compatible frequencies.

    There are promising products under development that could make solar energy more efficient. The solar panels seek to tap into the strengths of crystalline silicon and the 2nd generation PV technology. The most advanced third-generation solar panels include:

    Which Type of Solar Panels Should I Buy?

    There is no direct answer to this question without an evaluation of your situation. Some of the essential factors that affect the type of solar panels for your commercial or residential installation include:

    • Size of the roof or ground mounting space.
    • Budget.
    • Aesthetic preferences.
    • Size of the solar panel system.

    Monocrystalline solar panels are the most ideal if you have limited space. On the other hand, polycrystalline cells are suitable when low on the budget. Thin-film solar cells are the most common in power purchase agreements because of the short lifespan. They are also ideal for utility-scale or communal solar energy installations.

    Solar energy technology undergoes drastic changes in a short period because it is a developing technology. There are many feasibility studies to evaluate the application of different solar panels under review. Therefore, what is efficient today might be outdated within a year. You should keep an eye on the industry and do thorough research before settling for any solar panels.

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