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New record efficiency achieved with flexible solar cell

New record efficiency achieved with flexible solar cell

Currently, a large part of all solar modules consist of silicon solar cells , which are preferred over flexible solar cells made of polymer films due to their even higher efficiency. Scientists from the Swiss Federal Laboratory for Materials Testing and Research (Empa) have now introduced a flexible solar cell that sets a new record with an efficiency of 20.8 percent and thus approaches the efficiency of commercially used monocrystalline silicon solar cells, which is currently at a maximum of 22 percent lies.

In contrast to silicon solar cells, the advantage of polymer film solar cells is their high flexibility, which makes it possible to bend the organic solar cells and to manufacture them in many forms. For example, they can be integrated into clothing for the mobile generation of electricity .

CIGS solar cells are flexible and can therefore be used in a variety of ways. So far, their efficiency has been significantly lower than that of conventional silicon solar cells. An optimized variant of the Empa with a record efficiency of 20.8 percent no longer has this disadvantage.

The CIGS solar cell is ready for the market soon:

Flexible CIGS solar cells with lower efficiencies are already being used commercially. The developers of the new record-breaking solar cell hope that their optimized variant will also be launched on the market soon. As Tiwari explains, “Future developments will particularly aim to transfer our new process from the laboratory to the industrial scale in order to increase the power generation and profitability of photovoltaic systems .”

Thin-film solar cells with three improvements:

According to the research published in the specialist magazine Advanced Energy Materials, the higher efficiency could be achieved through three major developments of the previous technology. By optimizing the chemical composition of the absorber layer, the scientists have improved the electronic and optical properties of the solar cell.

Scientists at Empa set the previous record value of 18.7 percent for a flexible solar cell made of copper-indium-gallium-diselenide (CIGS) in 2011. According to Ayodhya Tiwari, the new peak achieved in the laboratory shows the potential of the technology that can now keep up with conventional, non-flexible solar cells.

In addition, the alkali metal doping process has been changed and the interface properties between the absorber and the buffer layer have been changed in order to increase the current generation by the thin-film solar cell.

Record Group Interviews:

Transcribing a group discussion is very time consuming and quite nerve-wracking. A good concentration is especially important when transcribing group conversations. The noise level in the recording is often higher and the conversations are usually more turbulent than in a “contemplative” two-way conversation.

To clarify: For the transcription of a conversation by two people, we calculate a transcription duration of 5-6 hours per hour interview. In group interviews with 8-10 hours of time per hour of interview.

With a few precautions, however, you can significantly reduce the later transcription effort and save unnecessary time. In this article we give you some useful tips and use sound examples to show how violently some effects can affect the sound quality  .

1. Avoid rumbling tables:

There is often a table in the middle of a discussion. So it makes sense to place the recording device there. But be careful: You probably know the effect of placing a swinging tuning fork on a table top? The table transmits the sound and resonates. The recording device is similar when you place it on the table. Paper rustling, tapping, writing, a projector or notebook nearby, spoons in coffee cups, pouring water … all these noises are transmitted directly to the recording device. Even if you do not notice them explicitly during the conversation – the recording device records them all. And listening to it afterwards is really uncomfortable. Our proposed solution:

Use a mini tripod or position the recording device on a book, a sweater or a hat or similar. to absorb vibrations from the table (writing,  tapping).
If dishes are unavoidable, make sure that the recording device is not near clattering cups.
Do not have a projector or similar nearby.

Here you can hear paper rustling and hectic notes from the secretary on the table – DM-650 on the table
And this is what it sounds like with a tripod – LS-12 on tripod

2. Correctly select level and format

To record a group as well as possible, the right recording device and the settings made on it are the most important factors. Please note:

If your device supports manual modulation, switch it on and level it well. If you are not sure: control it too quietly, the recordings can later be leveled out (made louder) with “Audacity” or “mp3 Gain”. Once too loud and thus overdriven and the recording is almost irretrievably  uncomfortable when listening.
The recording format should be .mp3 and be between 192 and 320 kB / s.

Please do not use .wma, .dss and or .m4a! Most recording devices, e.g. B. Philips DVT 4000, Olympus DM 650 and or LS 12, support various bit rates in .mp3 mode. If you have the choice, please always choose a fixed and non-variable bit rate. The latter can lead to different time stamps when using transcription programs and make it difficult to check or correct transcripts.
Quiet please – the room sounds too

The choice of location or space is crucial. As cozy as a beer garden is, but outside and with a lot of background noises is one of the worst conditions for group recording to enable a reasonably efficient transcription. You should also avoid very large, reverberant rooms. At the latest when the participants speak at the same time, only a “ballot” can be recorded, making a breakdown difficult. It is almost as important to influence the situation that secondary noises such as street noise through open windows or neighboring rooms are not recorded. Therefore:

  • Close the windows and doors and, if possible, only ventilate in phases.
  • Avoid taking pictures outdoors or use a fur windshield and manual control if it cannot be avoided.
  • Provide a calm environment. Conversations in the background or, for example, a café atmosphere are harmful.
  • Choose a room appropriate to the size of the group with as little reverberation as possible (carpet, curtains or a cloaked room are great).
  • Be careful not to place quiet speakers too far from the recording device.

4. Supported conversation

If you have made the preliminary planning for the recording of the group conversation, you can still do a lot on the day of the recording to make typing as pleasant as possible. This is especially true if the speakers are to be identified and identified throughout (i.e. Anna always as B1, Peter always as B2 or similar). From our experience in the transcription service we can give the following information:

Prepare a seating plan so that you can later localize voices on the recording based on the position of the recording device, the moderators / interviewers and the other people.
Luxury option: write down in a list of speakers in which order the people speak. WARNING: this is only useful if it is done consistently and closely enough.
If the topic and / or the research question allow, moderate the conversation to minimize overlaps and, above all, “wild” confusion.

Ask the participants to briefly introduce themselves in turn with their names and functions: the recording then provides reference points that can make it easier to identify the speaker later (very important, especially when outsourcing).

If you have a larger group, use a second recording device and have it recorded in parallel. This way you can listen to passages that are incomprehensible (from a different angle).

Here is an example of such a moderation – DM-650 on the table ( download )

Here again all pictures for comparison

For the following test recordings, we decided on four different recording devices that are used frequently. Olympus DM 650 (automatic control), an Olympus DS 7000 (dictation machine in .DSS format), iPhone 5S (.m4a format) and an LS 12 (manual control and mounted on a tripod). We used the Sony PCM-D100 as a reference for very high quality and comparatively expensive recording.

In the first sound examples, a lot of background noises can be heard and the speakers often cut themselves off. The second group discussion example is a guided moderation. What differences do you hear in the recordings? What do you find disturbing?

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